80mgf - furnaces

© 1998 Lennox Industries Inc.

Corp. 9801−L2

80MGFService Literature Revised 08−2004

80MGF SERIES UNITS80MGF series units are mid−efficiency gas furnaces

manufactured with tubular heat exchangers formed of alu-

minized or stainless steel. 80MGF units are available in

heating capacities of 45,000 to 140,000 Btuh and cooling

applications up to 5 tons. Refer to Engineering Handbook

for proper sizing.

Units are factory equipped for use with natural gas. A kit is

available for conversion to LPG operation. All 80MGF units

built proir to September 98 use electronic (direct spark) igni-

tion. 80MGF−11 model units are equipped with the Lennox

SureLight ignition system. The 80MGFX unit meets the

California Nitrogen Oxides (NOx) Standards and California

Seasonal Efficiency requirements. All units use a redun-

dant gas valve to assure safety shut−off as required by

A.G.A. or C.G.A.

The heat exchanger, burners and manifold assembly can

easily be removed for inspection and service by simply dis-

connecting gas, unplugging wiring harness and spark wires

and removing four screws holding the heat exchanger in

place. Then the heat exchanger slides out of the cabinet.

All specifications in this manual are subject to change.

Procedures outlined in this manual are presented as a rec-

ommendation only and do not supersede or replace local

or state codes. In the absence of local or state codes, the

guidelines and procedures outlined in this manual (except

where noted) are recommended only and do not constitute

code.

Units may be installed in upflow, downflow or horizontal

position. The heat exchanger is designed for upright or

horizontal use only. When the unit is installed in the down-

flow position, the heat exchanger is field removed and re-

installed so it is upright when the cabinet is inverted. No

field conversion is required when the unit is installed in the

horizontal position.

TABLE OF CONTENTS

Introduction 1. . . . . . . . . . . . . . . . . . . . . . . .

Specifications 2. . . . . . . . . . . . . . . . . . . . . .

Blower Data 5. . . . . . . . . . . . . . . . . . . . . . .

Parts Identification 7. . . . . . . . . . . . . . . . . .

I Unit Components 9. . . . . . . . . . . . . . . . . .

II Installation 19. . . . . . . . . . . . . . . . . . . . . . .

III Start Up 19. . . . . . . . . . . . . . . . . . . . . . . . .

Preliminary Seasonal Checks 20 . . . . .

Heating Start Up 20. . . . . . . . . . . . . . . .

IV Heating System Service Checks 20. . .

V Typical Operating Characteristics 22. . .

VI Maintenance 24. . . . . . . . . . . . . . . . . . . .

VII Wiring and Sequence of Operation 26.

VIII SureLight Control Troubleshooting 40.

SPECIFICATIONSModel No. 80MGF2(X)-45 80MGF2-60 80MGF3(X)-60 80MGF2-75 80MGF3(X)-75

Input Btuh (kW) 45,000 (13.2) 60,000 (17.6) 75,000 (22.0)

Output Btuh (kW) 36,900 (10.8) 49,200 (14.4) 61,700 (18.1)

�A.F.U.E. 80.1% 80.5% 80.1% 80.0%

California Seasonal Efficiency 75.4% 76.4% 75.9% 76.8% 76.8%

Flue size connection diameter � in. (mm) round 3 (76) 4 (102)

Temperature rise range � �F (�C) 30 - 60 (17 - 33) 45 - 75 (25 - 42)

High static certified by A.G.A./C.G.A. � in wg. (Pa) .50 (125)

Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13)

Blower wheel nominaldi t idth

in. 9 x 7 10 x 7 9 x 7 10 x 7Blower wheel nominal

diameter x widthmm 229 x 178 254 x 178 229 x 178 254 x 178

Blower motor output � hp (W) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224)

Nominal coolingth t b dd d

Tons 1, 1-1/2 or 2 2, 2-1/2 or 3 1, 1-1/2 or 2 2, 2-1/2 or 3Nominal cooling

that can be addedkW 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6 3.5, 5.3 or7.0 7.0, 8.8 or 10.6

Shipping weight � lbs. (kg) 1 package 130 (59) 135 (61)

Electrical characteristics 120 volts � 60 hertz � 1 phase (less than 12 amps) All models

� Optional Accessories (Must Be Ordered Extra) �

LPG/propane kit LB-69845L (38K84)

Twinning Kit 15L3801 � 5 lbs. (2 kg)

Up−Flow/Horizontal Filter and Filter Rack Kits�N & i f filt i ( )

Single (32J02) Ten Pack (66K64)Up Flow/Horizontal Filter and Filter Rack Kits�No. & size�of�filters�− in. (mm)

Single (32J02) Ten Pack (66K64)(1) 16 x 20 x 1 (406 x 508 x 25)

�Down-flowFilt Kit

Catalog No. LB-69843A (32J01) � 3 lbs. (1 kg)�Down flow

Filter KitNo. & Size of Filters � in. (mm) (2) 16 x 20 x 1 (406 x 508 x 25)

Down-flow Combustible Floor Base LB-79239A (67J91) � 10 lbs. (4 kg)

Sidewall Power Venting Kit 79J15 � 25 lbs. (11 kg)

Hanging Bracket Kit LB-69957 (46J66) � 15 lbs. (8 kg)

�Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherizedfurnaces.

�Polyurethane frame type filter is furnished with kit.�Filters are not furnished with kit and must be ordered extra.

SPECIFICATIONS continuedModel No. 80MGF4(X)-75 80MGF3/4(X)-100 80MGF4/5(X)-100

Input Btuh (kW) 75,000 (22.0) 100,000 (29.3)

Output Btuh (kW) 61,700 (18.1) 82,000 (24.0)

�A.F.U.E. 80.0% 80.1% 80.0%

California Seasonal Efficiency 76.3% 76.5% 77.0%

Flue size connection diameter � in. (mm) round 4 (102)

Temperature rise range � �F (�C) 45 - 75 (25 - 42) 35 - 65 (19 - 36)

High static certified by A.G.A./C.G.A. � in wg. (Pa) .50 (125) .65 (162)

Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13)

Blower wheel nominaldi t idth

in. 12 x 8 12 x 9Blower wheel nominal

diameter x widthmm 305 x 203 305 x 229

Blower motor output � hp (W) 1/2 (373) 3/4 (560)

Nominal coolingth t b dd d

Tons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6Nominal cooling

that can be addedkW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1




LPG/propane kit LB-69845L (38K84) LB-69845K (81J14)


Up−Flow/Horizontal Filter and Filter Rack Kits Single (32J02) Ten Pack (66K64) Single (46J14) Ten Pack (66K65)Up Flow/Horizontal Filter and Filter Rack Kits�No. & size�of�filters�− in. (mm)



�Down-flowCatalog No. LB-69843A (32J01) � 3 lbs. (1 kg)

�Down flowFilter Kit No. & Size of Filters � in. (mm) (2) 16 x 20 x 1 (406 x 508 x 25)

Down-flow Combustible floor Base LB-79239A (67J91) � 10 lbs. (4 kg) LB-79239B (67J92) � 10 lbs. (4 kg)



�Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherizedfurnaces.

�Polyurethane frame type filter is furnished with kit.�Filters are not furnished with kit and must be ordered extra.

SPECIFICATIONS continued

Model No. 80MGF3/4-120 80MGF4/5(X)-120 80MGF4/5-140

Input Btuh (kW) 120,000 (35.2) 140,000 (41.0)

Output Btuh (kW) 98,400 (28.8) 114,800 (33.6)

�A.F.U.E. 80.0% 80.1% 80.0%

California Seasonal Efficiency Not Available 75.5% Not Available

�Flue size connection diameter � in. (mm) round 4 (102) 5 (127)

Temperature rise range � �F (�C) 45 - 75 (25 - 42)

High static certified by A.G.A./C.G.A. � in wg. (Pa) .50 (125) .65 (162)

Gas Piping Size I.P.S. Natural or LPG/propane in. (mm) 1/2 (13)

Blower wheel nominalin. 12 x 8 12 x 9

Blower wheel nominaldiameter x width mm 305 x 203 305 x 229

Blower motor output � hp (W) 1/2 (373) 3/4 (560)

Nominal coolingTons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6

Nominal coolingthat can be added kW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1




LPG/propane kit LB-69845K (81J14)


Up−Flow/Horizontal Filter and Filter Rack Kits�No. & size�of�filters�− in. (mm



Catalog No. LB-69843A (32J01) � 3 lbs. (1 kg)

�Down-flowFilter Rack No. & Size

in. (2) 16 x 20 x 1Filter Rack No. & Size

of Filters mm (2) 406 x 508 x 25

Down-flow Combustible Floor Base LB-79239B (67J92) � 10 lbs. (4 kg) LB-79239C (67J93) � 12 lbs. (5 kg)



�Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces. �Polyurethane frame type filter is furnished with kit.�2 in. x 5 in. (51 mm x 127 mm) flue adaptor furnished with -140 input furnaces for connection to furnace induced draft blower.�Filters are not furnished with kit and must be ordered extra.

BLOWER PERFORMANCE DATA

80MGF2-45, 80MGF2-60 AND 80MGF2-75 BLOWER PERFORMANCE

External Static Air Volume at Various Blower SpeedsExternal StaticPressure High Medium-High Medium-Low Low

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s

0 0 1270 600 980 460 770 365 570 270

.05 12 1245 590 975 460 770 365 565 265

.10 25 1220 575 975 460 770 365 565 265

.15 37 1195 565 965 455 765 360 560 265

.20 50 1170 550 960 455 760 360 560 265

.25 62 1140 540 950 450 760 360 555 260

.30 75 1110 525 940 445 760 360 550 260

.40 100 1060 500 910 430 750 355 545 255

.50 125 990 465 880 415 740 350 540 255

.60 150 900 425 810 380 690 325 530 250

.70 175 800 380 740 350 630 295 520 245

NOTE � All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

80MGF3-60 AND 80MGF3-75 BLOWER PERFORMANCE

External Static Air Volume at Various Blower SpeedsExternal StaticPressure High Medium-High Medium-Low Low

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s

0 0 1425 670 1240 585 1000 470 800 380

.05 12 1415 670 1230 580 995 470 800 380

.10 25 1400 660 1220 575 990 465 795 375

.15 37 1385 655 1200 565 985 465 795 375

.20 50 1370 645 1180 555 980 460 790 375

.25 62 1350 635 1160 545 970 460 780 370

.30 75 1330 630 1140 540 955 450 770 365

.40 100 1280 605 1095 515 925 435 750 355

.50 125 1210 570 1040 490 900 425 720 340

.60 150 1135 535 985 465 860 405 680 320

.70 175 1070 505 920 435 800 380 630 300


80MGF4-75, 80MGF3/4-100 AND 80MGF3/4-120 BLOWER PERFORMANCE

External StaticAir Volume at Various Blower Speeds

External StaticPressure High Medium-High Medium Medium-Low Low

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s

0 0 1830 865 1600 755 1325 625 1070 505 880 415

.05 12 1815 855 1585 750 1320 625 1070 505 880 415

.10 25 1800 850 1570 740 1315 620 1070 505 880 415

.15 37 1875 885 1550 730 1310 620 1065 505 875 415

.20 50 1750 825 1530 720 1300 615 1060 500 875 415

.25 62 1725 815 1515 715 1290 610 1050 495 870 410

.30 75 1700 800 1500 710 1275 600 1040 490 870 410

.40 100 1650 780 1460 690 1245 590 1020 480 860 405

.50 125 1600 755 1420 670 1210 570 1000 470 840 395

.60 150 1550 730 1380 650 1170 550 980 460 820 385

.70 175 1480 700 1330 630 1130 535 960 455 790 375


80MGF4/5-100, 80MGF4/5-120 AND 80MGF4/5-140 BLOWER PERFORMANCE

External StaticAir Volume at Various Blower Speeds

External StaticPressure High Medium-High Medium Medium-Low Low

in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s

0 0 2450 1155 2160 1020 1970 930 1700 800 1500 710

.05 12 2440 1150 2155 1015 1965 925 1695 800 1500 710

.10 25 2430 1145 2150 1015 1960 925 1690 800 1495 705

.15 37 2415 1140 2135 1010 1950 920 1685 795 1495 705

.20 50 2400 1135 2120 1000 1940 915 1680 795 1490 705

.25 62 2380 1125 2105 995 1930 910 1675 790 1480 700

.30 75 2360 1115 2090 985 1915 905 1670 790 1470 695

.40 100 2310 1090 2050 965 1870 880 1650 780 1440 680

.50 125 2260 1065 2000 945 1810 855 1610 760 1410 665

.60 150 2180 1030 1950 920 1750 825 1560 735 1370 645

.70 175 2100 990 1890 890 1700 800 1520 715 1330 630


FILTER AIR RESISTANCE

cfm (L/s) in. w.g. (Pa)

0 (0) 0.00 (0)

200 (95) 0.01 (2)

400 (185) 0.03 (7)

600 (280) 0.04 (10)

800 (375) 0.06 (15)

1000 (470) 0.09 (22)

1200 (560) 0.12 (30)

1400 (655) 0.15 (37)

1600 (750) 0.19 (47)

1800 (845) 0.23 (57)

2000 (935) 0.27 (67)

2200 (1030) 0.33 (82)

2400 (1125) 0.38 (95)

2600 (1220) 0.44 (110)

FIGURE 1

80MGF PARTS IDENTIFICATIONand ORIENTATION VENT ADAPTER

CABINET TOP

80MGFCABINET

CABINETBOTTOM

HEAT EXCHANGERASSEMBLY

BURNERASSEMBLY

BLOWER ASSEMBLY

COMBUSTION AIRBLOWER

FLUE BOX

SECONDARYLIMITS

FRONT ACCESSPANEL

DOOR INTERLOCK SWITCH

CONTROLBOARD

TRANSFORMER

PRESSURESWITCH

NOxTURBULATOR

PRIMARYLIMIT

FIGURE 2

HEATING COMPONENTS (shown in horizontal position)

HEAT EXCHANGER

COMBUSTION AIR BLOWER

MANIFOLD

ROLLOUT SWITCH (2)

COMBUSTION AIRPROVE SWITCH

GAS VALVE

BURNERS

COLLECTOR

PRIMARY LIMIT

Front

Right

Top

Bottom

Left

Back

FIGURE 3

Top

80MGF BURNER ASSEMBLY (Shown With SureLight ignitor)

FLAMESENSOR

MANIFOLD

ORIFICE

GAS VALVE

HEAT EXCHANGER

VEST PANEL

BURNER

UPPERBURNER

MOUNTINGRAIL

LOWERBURNER

MOUNTINGRAIL

BURNER BOX

BURNER BOXTOP

FrontRight

Bottom

LeftBack

PRIMARY LIMIT

ROLLOUTSWITCHES

SURELIGHT IGNITOR

FIGURE 4

80MGF BLOWER DOOR COMPONENTS − BLOWER ACCESS(SureLight MODEL SHOWN)

1

5

8

To Access Blower:

1− Turn off power to unit and disconnect L1 and L2line voltage power.

2− Disconnect thermostat wiring connectionsfrom furnace control board.

3− Disconnect blower leads from control board.

4− Disconnect J1 from P1.

5− Disconnect 6 pin P156 from control board.

6− Disconnect 9 pin P58 from control board.

7− Disconnect sensor wiire from center of board.

8− Remove screws (2) and lift panel from unit.

2

Top

Bottom

Left

Right

Front

3

4

6

Back

7

I−UNIT COMPONENTS (Figures 1, 2, 3)

80MGF unit components are shown in figure 1. The blower

controls, gas valve and burners can be accessed by re-

moving the front access panel. A separate blower access

door is located behind the front access panel. Electrical

control components are mounted to the blower access

door.

80MGF units are factory equipped with bottom return air pan-

els. The panels are designed to be field removed as required

for bottom air return. Indentations on side of units, show

where side air return opening should be cut during installation.

A−Blower Door Components (Figure 4)Electrical burner control and blower control components

are located on the outside surface of the blower access

door. Jackplugs allow the blower door to be easily re-

moved for blower service.

Located on the blower door are the unit transformer (T1),

the furnace control (A3) and door interlock switch (S51).

Furnace control (A3) combines the function of a burner

ignition control and blower control.

1− Control Transformer (T1)

A transformer located on the blower door provides power

to the low voltage section of the unit. Transformers on all

models are rated 30VA with a 120V primary and a 24V sec-

ondary.

2−Door Interlock Switch (S51)

A door interlock switch rated 16A at 125VAC is located on

the blower access door. The switch is wired in series with

line voltage. When the blower door is removed the unit will

shut down.

3− Ram Control (A3)The furnace control combines burner ignition functions

with blower control functions.

Some early model 80MGF units utilize a furnace control

manufactured by RAM Electronics Corporation. The �RAM"

board is a printed circuit board which controls the blower, gas

valve, combustion air blower and ignition spark. It also moni-

tors the flame, limit and gas valve operation. The control has

a non−adjustable, factory preset �on" fan timing (45 sec-

onds). Fan �off" timings are adjustable. The board utilizes

both 120 and 24VAC. See figure 5. The board is also

equipped with a diagnostic LED for use when troubleshoot-

ing the unit.

When the furnace is idle (blower off and no heating or cool-

ing demand), the diagnostic LED flashes at a slow steady

rate. On a call for heat, the diagnostic LED begins flashing

at a fast rate and the combustion air blower is energized.

The LED flashes different codes to indicate problem con-

ditions. The diagnostic LED lights red (not flashing) to indi-

cate control board failure. Table 3 shows how to interpret the

other LED modes.

Pre-Purge

On a call for heat, the combustion air blower begins oper-

ating. If the combustion air prove switch closes, the com-

bustion air blower continues to operate for 45 seconds

(pre-purge) before allowing ignition. Pre-purge allows the

heat exchanger to be cleared of combustion products and

to introduce fresh air for combustion. If the combustion air

prove switch does not close, the combustion air blower

continues to run indefinitely (until the prove switch closes).

Post-Purge

After a demand, the combustion air blower continues to

operate for 5 seconds (post-purge) before stopping. Post-

purge allows the heat exchanger to be cleared of combus-

tion products.

Ignition Control

The ignition control is a direct spark ignition control module

integral to the furnace control. See figure 5. When there is a

call for heat, the control delays ignition until combustion air

blower operation has been proved and pre-purge period

has elapsed. It then opens the gas valve and generates a

spark to ignite the burners. Trial for ignition lasts for 7 sec-

onds. At the same time, the control begins monitoring the

flame sensor. If the flame current is too weak (less than 1

microamp) or if the burners do not ignite (within the 7 sec-

ond ignition trial), the control will shut off spark and the com-

bustion air blower and de-energize the gas valve. Flame

current should be between 1 and 5 microamps to keep the

gas valve open. See figure 23.

The control will attempt to ignite the burners up to two more

times. Each time the control restarts the ignition sequence,

it begins with a 45 second pre-purge. If flame is not sensed

after the third trial, the control locks out. Lockout means that

the control shuts off the gas valve, spark and combustion air

blower for 60 minutes. At the end of 60 minutes the control

completely resets and will attempt ignition up to three times.

The control can be manually reset before the end of 60 min-

utes by momentarily turning off power to the unit.

DANGERShock hazard.

Spark related components contain high voltage.Disconnect power before servicing. Control isnot field repairable. If control is inoperable, sim-ply replace entire control.

Can cause injury or death. Unsafe operation willresult if repair is attempted.

RAM CONTROL (A3)

FIGURE 5

LINE VOLTAGETERMINAL

CONNECTIONS

24VAC VOLTTERMINAL

CONNECTIONS

THERMOSTATCONNECTIONS

DIAGNOSTICLED

See Table 2 forTerminal Func-

tions

See Table 2 forTerminal Func-

tions

FAN-OFF TIMINGSWITCHES

SPARK OUTPUT

TABLE 1

Furnace Control A3 Limit Response During Operation

Response

ConditionCombustion

AirBlower

GasValve

SupplyAir

Blower

DiagnosticLED

Loss of FlameSensed BeforeEnd of 45 sec-ond Blower On

Delay(3 or Fewer

Trialsfor Ignition)

On

On(SparkStarts

Within 0.8seconds)

On Fast Flash

Loss of FlameSensed After

45 secondBlower OnDelay (3 or

Fewer Trialsfor Ignition)

On

Off ThenOn WithSpark

After Pre-Purge

On Fast Flash

Loss of FlameSensed (MoreThan 3 Trialsfor Ignition)

Off Off Off 2 Flashes

Flame SensedWithoutDemand

On Off On 5 Flashes

Primary or Sec-ondary Limit

OpenOn Off On 4 Flashes

Rollout SwitchOpen

On Off On 4 Flashes

Combustion AirProve Switch

OpenOn Off On 3 Flashes

When flame is sensed, the indoor blower starts after a 45

second delay. Gas valve remains open and blower contin-

ues to run until demand stops, flame sensor senses loss of

flame, a limit opens or the prove switch opens. If any of

these events occur during a thermostat demand, the gas

valve closes and the diagnostic LED registers the error

condition (table 1).

Blower Control and Timings

DANGERElectrical Shock Hazard.This control contains field adjustable switchesand also contains line voltage. Make sure poweris disconnected before making any field adjust-ments or performing any service procedure.

NOTE�If fan �off" time is set too low, residual heat in

heat exchanger may cause primary limit S10 to trip re-

sulting in frequent cycling of blower. If this occurs, ad-

just blower to longer time setting.

Fan �ON" timing (time that the burners operate before the

supply air blower starts) is fixed at 45 seconds and cannot

be adjusted.

Fan �OFF" timings (time that the blower operates after a

heating or cooling demand has been satisfied) are de-

termined by the arrangement of switches on the furnace

control board. See figure 5. To adjust fan �off " timings,

gently reposition the switches to a new timing position.

Figure 6 shows the various fan �off" timings and how

switches should be positioned. 80MGF−1, −2, −3, −4 and −6

units are shipped with a factory fan �off" setting of 180 sec-

onds. 80MGF−5 and −7 units are shipped with factory "off"

setting of 60 seconds. Fan �off" time will affect comfort and

efficiency and is adjustable to satisfy individual applica-

tions. The fan �off" timing is initiated after a heating or cool-

ing demand but not after a blower demand (that is, when

indoor thermostat switch is changed from ON to AUTO

and heating/cooling demand is not present, the blower

stops immediately).

TABLE 2

FURNACE CONTROL A3 TERMINAL DESIGNATIONS

Terminal Type Function

Y Screw Strip Cooling Demand

G Screw Strip Blower Demand

R Screw Strip 24VAC to Thermostat

W Screw Strip Heating Demand

C

Early Units1/4" Spade

24VAC CommonCLater UnitsScrew Strip

24VAC Common

120VAC HOT 1/4" Spade Line Voltage In

AUX 1/4" Spade Line Voltage Out (Switched)

CMB BLWR 1/4" SpadeSwitched 120VAC to

Combustion Air Blower

ACB HEAT 1/4" SpadeSwitched 120VAC toBlower Heating Tap

ACB COOL 1/4" SpadeSwitched 120VAC to Blower

Cooling Tap

VALVE 1/4" Spade 24VAC to Gas Valve

24VAC HOT 1/4" Spade 24VAC In From Transformer

GROUND 1/4" Spade To Cabinet Ground

FLAME SENSE 1/4" Spade Flame Microamp Sensing

PSW 1/4" Spade24VAC In From Pressure SwitchSwitch Open: Prohibits IgnitionSwitch Closed: Allows Ignition

HI LIMIT IN 1/4" Spade24VAC In From Limits

Limit Open: Closes Gas ValveLimits Closed: Allows Ignition

HI LIMIT OUT 1/4" Spade24VAC to Limit Trainand Pressure Switch

ROLLOUT IN 1/4" Spade 24VAC In From Rollout Switches

FIGURE 6

FAN-OFF TIME ADJUSTMENT SWITCHESLOCATED ON FURNACE CONTROL (A3)

Fan-Off Timings

Switch

1 2

TimingSeconds

Off

OnOff

Off

OffOn

On On

120

90

180

240

Diagnostic LED

The furnace control is equipped with a diagnostic LEDused for troubleshooting the unit and the control. LEDfunctions are shown in table 3.

TABLE 3

Furnace Control A3 Diagnostic LED

LED State Meaning Remedy

Steady On Control Failure Replace Control

Slow FlashNormal Operation and

No Call For Heat- - - -

Fast FlashNormal Operation with

Call For Heat- - - -

TwoFlashes

Control Lockout

Failed to Sense or SustainFlame. Check Gas Valve,Burners, Spark Electrodeand Wire, Flame Sensor.Replace Control If All OK.

ThreeFlashes

Pressure Switch Open

Failed to Prove Combus-tion Blower Operation orBlocked Vent. Repair orReplace as Necessary.

FourFlashes

Open Limit

Check Primary Limit, RolloutSwitches and Secondary

Limits. Find source of Over-temperature. If all OK, Resetor Replace Limits as Neces-

sary.

FiveFlashes

Flame Sensed and GasValve Not Energized.

Check Gas Valve. If OK,Check Flame Sensor.

4− EGC Control (A3)Some early model 80MGF units are equipped with an inte-

grated ignition/blower control (EGC−1 or EGC−2) which con-

trols ignition, safety circuits, blower operation, fan off timing,

and allows for thermostat connection and troubleshoot-

ing. The EGC is a printed circuit board which is divided

into two sections, 120 and 24VAC. Line voltage comes

into the board on the 120VAC side. See figure 8. Terminal

designations are listed in tables 5 and 6.

Ignition Control

80MGF units use the EGC direct spark integrated igni-

tion control. The EGC controls and monitors the entire

sequence of operation. On a call for heat from the ther-

mostat the control monitors the combustion air blower

pressure switch. The control will not begin the heating

cycle if the pressure switch is closed (by-passed). Once

the pressure switch is determined to be open, the combus-

tion air blower is energized. When the differential in pres-

sure across the pressure switch is great enough, the pres-

sure switch closes and a 15 second pre-purge period

begins. After the pre-purge period, the gas valve will open

and ignition (spark) will be attempted for 10 seconds. After

ignition, the control initiates a ten second flame stabiliza-

tion period. The flame stabilization period allows the

burners to heat up and the flame to stabilize. Once flame

is established, the control will constantly monitor the burner

flame using flame rectification. Flame failure response time is

0.8 seconds.

If the initial attempt for ignition fails, the sequence is re-

peated up to five times. After the fifth trial, the control goes into

�Watchguard"*. During watchguard mode, the entire unit will

be de-energized for one hour. After one hour the control will

repeat the ignition sequence. Watchguard may be manually

reset by breaking and remaking thermostat demand.

*NOTE−If flame is established beyond the 10 second flame

stabilization period then lost, the control resets for five more

ignition trials. The control can be reset five times during one

unsatisfied thermostat demand, providing a maximum

of 25 trials for ignition.

Safety Circuits

During the entire heating demand the control monitors the

safety circuits. If the primary or secondary heating limits

open, the control de-energizes the main gas valve and

combustion air blower while the indoor blower remains en-

ergized. When the limit automatically resets, the ignition se-

quence also resets. If either of the limits trip five consecu-

tive times during one unsatisfied thermostat demand, the

control will go into watchguard for one hour.

The control monitors main valve voltage. If voltage is sensed

when no voltage should be present, the control de-energizes

the combustion air blower which terminates voltage to the

valve. The system goes into hard lock-out which is reset only

by removing power to the unit.

If flame is sensed when no flame should be present, the con-

trol will energize the combustion and indoor blowers. The

unit will remain locked in this sequence until the flame is no

longer sensed or the main power is turned off to reset the

control.

DANGERShock hazard. Avoid personal injury. Make sure todisconnect power before changing fan �off" timing.

Blower Operation / Fan Off Timings

Fan �off" timing (time that the blower operates after the heat

demand has been satisfied) can be adjusted by moving the

jumper on the EGC blower control board. Figure 7 shows

the various fan �off" timings and how jumper should be posi-

tioned. To adjust fan �off " timing, gently disconnect jumper

and reposition across pins corresponding with new timing.

Unit is shipped with a factory fan �off" setting of 180 seconds.

Fan �on" time is factory set at 45 seconds following the

opening of the main gas valve and is not adjustable.

Fan �off" time will affect comfort and efficiency and is ad-

justable to satisfy individual applications. The fan �off" tim-

ing is initiated after a heating demand but not after a cool-

ing demand.

NOTE�If fan �off" time is set too low, residual heat in

heat exchanger may cause primary limit S10 to trip, re-

sulting in frequent cycling of blower. If this occurs, adjust

blower to longer fan �off" time setting.

FIGURE 7

FAN-OFF TIME ADJUSTMENT

180 60

120 90

To adjust fan-off timing:Remove jumper from EGC and select oneof the other pin combinations to achieve

the desired time.

TIMINGJUMPER

TIMING PINS(seconds)

Leave jumper off for240 second fan-off timing.

Thermostat Connection

Thermostat wires are connected to the terminal strip

found on the EGC control board.

Troubleshooting

The EGC control board is equipped with two diagnostic green

LEDs to indicate the mode of failure. The LED lights are

marked DIAG #1 and DIAG #2. The codes are given in table

4. On the EGC−1 only, the last failure code is stored in

memory and may be retrieved by depressing and holding

the memory recall button. When this button is depressed,

the LEDs will signal the last failure code in memory. Power

must be restored to the control (depress blower interlock

switch) within one minute of blower access panel removal in

order to retain memory. To clear the memory of the stored

failure code, remove main power and short the jumper next

to the diagnostic button for five seconds.

TABLE 4

EGC DIAGNOSTIC CODES

DIAG #2 DIAG #1 DIagnostic Condition

SimultaneousFlash

SimultaneousFlash

Power �ON". Normal Operation. In-creased flash rate indicates there

is a heating demand.

On FlashPrimary or Secondary

Limit Switch Open.Auto-Reset Switch.

Flash Off

Pressure Switch Watchguard,pressure switch opened during

operation or condensatedrain blocked.

AlternateFlash Alternate Flash

Watchguard, burnersfailed to ignite.

Off FlashFlame sensed without

valve energized.

Flash OnRoll-out Switch Open.Manual-Reset Switch.

ContinuousOn Continuous On

Circuit board self-check failure orignition/blower controlis wired incorrectly.

FIGURE 8

EDGECONNECTION

THERMOSTATTERMINAL STRIP(DETACHABLE)

BLOWER TIMEADJUSTMENT

JUMPER

DIAGNOSTIC MODULE

DIAGNOSTIC LEDS

RED DIAGNOSTIC BUTTON(EGC−1 only. Depress button and hold

for display of last failure code.)

DIAGNOSTIC CODE ERASE JUMPER(Remove power to control and short pins for

10 seconds to erase previous code.)

24VACPLUG P20

5

6

7

8 9 10 11 12 13 15

123

4

14 16

1

2

3

4

6

5

7

8

9

EGC−2 INTEGRATED CON-TROL

NOTE: EGC−1 board will have terminal (#15) forACB low speed.

*

*

**

** NOTE: EGC−1 board will have terminal(#16) for ACB Heat speed.

TABLE 5BLOWER CONTROL A15 TERMINAL DESIGNATIONS

TerminalDesignation(See fig. 8)

Type Function

R Screw Strip 24VAC to Thermostat (Red)

G Screw StripManual Fan Input from Thermostat

(Green)

W Screw StripHeat Demand Input from Thermostat

(White)

Y Screw StripCool Demand Input from Thermostat

(Yellow)

C Screw Strip Common Ground to Thermostat

1 1/4" Spade 24VAC Hot from Transformer

2 1/4" Spade 24VAC Return to Transformer

3 1/4" Spade 24VAC Ground

4, 5, 6 1/4" Spade 120VAC Return − 120VAC Common

7 1/4" Spade120VAC Return − 120VAC Common

Input

8 1/4" Spade Combustion Blower (Line Voltage)

9 1/4" Spade Heat Only Accessory (Line Voltage)

10 1/4" Spade 120VAC Hot to Transformer

11 1/4" Spade 120VAC Hot Input

12, 13 1/4" Spade Accessories (Line Voltage)

14 1/4" Spade ACB Cool Speed (Line Voltage)

15 1/4" Spade

EGC−1 ACB Low Cont. Speed (Line Voltage)

EGC−2 ACB Heat Speed (Line Voltage)

16 1/4" Spade ACB Heat Speed (Line Voltage)

TABLE 6

EGC CONTROL JACK/PLUG 20 TERMINAL DESIGNATIONS

Pin # Function

1 Rollout Switch Out

2 Spare

3 Gas Valve Common

4 Pressure Switch Return

5 Hi Limit Return / Pressure Switch Out

6 Flame Sensor

7 Gas Valve Out

8 High Limit Out

9 Rollout Switch Return

DANGERShock hazard.

Disconnect power before servicing. Control is notfield repairable. If control is inoperable, simplyreplace entire control.

Can cause injury or death. Unsafe operation willresult if repair is attempted.

5−Flame Sensor (−11 models)A flame sensor is located on the left side of the burner sup-

port. See figure 9. The sensor is mounted on a bracket in

the burner support and the tip protrudes into the flame en-

velope of the left−most burner. The sensor is fastened to

burner supports and can be removed for service without

removing any part of the burners. During operation, flame

is sensed by current passed through the flame and sens-

ing electrode. The SureLight control allows the gas valve

to remain open as long as flame signal is sensed.

FIGURE 9

NORMAL FLAME SIGNAL � 0.7 MICROAMPSLOW FLAME SIGNAL � 0.7 MICROAMPSMINIMUM FLAME SIGNAL � 0.15 MICROAMPS

BURNER

FLAMESENSORSIDE VIEW END VIEW

1/4 in. 7 mm� 1/32 in. 0.79

mm

3/16 in.4.7 mm

11/16 in. 18 mm� 1/32 in. 0.79

mm

NOTE − The 80MGF furnace contains electronic com-

ponents that are polarity sensitive. Make sure that the

furnace is wired correctly and is properly grounded.

6− SureLight Ignition System A3 (−11 models)

All 80MGF−11 model units are equipped with the LennoxSureLight ignition system. The system consists of ignitioncontrol board (figure 11 with control terminal designa-tions in table 10) and ignitor (figure 12). The board and ig-nitor work in combination to ensure furnace ignition andignitor durability. The SureLight integrated board controlsall major furnace operations. The board also features twoLED lights for troubleshooting and two accessory termi-nals rated at (4) four amps. See table 9 for troubleshoot-ing diagnostic codes. Table 7 and 8 show jack plug termi-nal designations. Units equipped with the SureLightboard can be used with either electronic or electro−me-chanical thermostats without modification. The SureLightignitor is made of durable silicon−nitride. Ignitor longevityis also enhanced by voltage ramping by the control board.The board finds the lowest ignitor temperature which willsuccessfully light the burner, thus increasing the life of theignitor.

TABLE 7

SureLight BOARD J156 (J2) TERMINAL DESIGNATIONS

PIN # FUNCTION

1 Ignitor

2 Not Used

3 Ignitor Neutral

4 Combustion Air Blower Line Voltage

5 Not Used

6 Combustion Air Blower Neutral

TABLE 8

SureLight BOARD J58 (J1) TERMINAL DESIGNATIONS

PIN # FUNCTION

1 Primary Limit In

2 Gas Valve Common

3 Roll Out Switch Out

4 Gas Valve 24V

5 Pressure Switch In

6 Pressure Switch and Primary Limit Out

7 Not Used

8 Roll Out Switch In

9 Ground

CAUTIONElectrostatic discharge can affect electroniccomponents. Take precautions during furnaceinstallation and service to protect the furnace’selectronic controls. Precautions will help to avoidcontrol exposure to electrostatic discharge byputting the furnace, the control and the techni-cian at the same electrostatic potential. Neutral-ize electrostatic charge by touching hand and alltools on an unpainted unit surface, such as thegas valve or blower deck, before performing anyservice procedure.

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures

a−Electronic IgnitionOn a call for heat the SureLight control monitors the com-

bustion air blower pressure switch. The control will not be-

gin the heating cycle if the pressure switch is closed (by−

passed). Once the pressure switch is determined to be

open, the combustion air blower is energized. When the

differential in the pressure switch is great enough, the

pressure switch closes and a 15−second pre−purge be-

gins. If the pressure switch is not proven within 2−1/2 min-

utes, the control goes into Watchguard−Pressure Switch

mode for a 5−minute re−set period.

After the 15−second pre−purge period, the SureLight igni-

tor warms up for 20 seconds after which the gas valve

opens for a 4−second trial for ignition. 80MGF units with

board 63K89, 24L85 or 56L83: the ignitor stays energized

for the first second of the 4−second trial. Units with board

97L48: ignitor stays energized for the full 4−second trial for

ignition. If ignition is not proved during the 4−second peri-

od, the control will try four more times with an inter purge

and warm−up time between trials of 35 seconds. After a to-

tal of five trials for ignition (including the initial trial), the

control goes into Watchguard−Flame Failure mode. After a

60−minute reset period, the control will begin the ignition

sequence again.

The SureLight control board has an added feature that

prolongs the life of the ignitor. After a successful ignition,

the SureLight control utilizes less power to energize the ig-

nitor on successive calls for heat. The control continues to

ramp down the voltage to the ignitor until it finds the lowest

amount of power that will provide a successful ignition.

This amount of power is used for 255 cycles. On the 256th

call for heat, the control will again ramp down until the low-

est power is determined and the cycle begins again.

b−Fan Time Control

The fan on time of 45 seconds is not adjustable. Fan off

time (time that the blower operates after the heat demand

has been satisfied) can be adjusted by flipping the dip

switches located on the SureLight integrated control. The

unit is shipped with a factory fan off setting of 90 seconds.

Fan off time will affect comfort and is adjustable to satisfy

individual applications. See figure 10.

FIGURE 10

FAN-OFF TIME ADJUSTMENT

To adjust fan−off timing, flip dip switch to desired setting.

60sec. 90sec. 120sec. 180sec.

The SureLight board is equipped with two LED lights for troubleshooting. The lights are found just above the 24VAC termi-

nal strip see figure 8. The diagnostic codes are listed below in table 9.

TABLE 9 DIAGNOSTIC CODES

MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT.

LED #1 LED #2 DESCRIPTION

SIMULTANEOUSSLOW FLASH

SIMULTANEOUSSLOW FLASH

Power − Normal operationAlso signaled during cooling and continues fan.

SIMULTANEOUS FASTFLASH

SIMULTANEOUS FASTFLASH

Normal operation − signaled when heating demand initiated at thermostat.

SLOW FLASH ON

Primary or Secondary limit open. Units with board 63K8901 or 24L85: Limit mustclose within 5 trials for ignition or board goes into one hour limit Watchguard.Units with board 56L83 or 97L48: Limit must close within 3 minutes or board

goes into one hour limit Watchguard.

OFF SLOW FLASH

Pressure switch open or has opened 5 times during a single call for heat; OR:Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switch

closed prior to activation of combustion air blower.

ALTERNATING SLOWFLASH

ALTERNATING SLOWFLASH

Watchguard − burners fail to ignite.

SLOW FLASH OFF Flame sensed without gas valve energized.

ON SLOW FLASH Rollout switch open. OR: 9 pin connector improperly attached.

ONONOFF

ONOFFON

Circuit board failure or control wired incorrectly.

FAST FLASH SLOW FLASH Main power polarity reversed. Switch line and neutral.

SLOW FLASH FAST FLASH Low flame signal. Measures below .7 microAmps. Replace flame sense rod.

ALTERNATING FASTFLASH

ALTERNATING FASTFLASH

Improper main ground or line voltage below 75 volts; OR: Broken ignitor; OR:Open ignitor circuit.

NOTE − Slow flash equals 1 Hz (one flash per second). Fast flash equals 3 Hz (three flashes per second). Drop out flame sense current < 0.15 microAmps

SURELIGHT INTEGRATED CONTROL BOARD

FIGURE 11

FIGURE 12

SURELIGHT IGNITOR

SureLight Ignitor

TABLE 10

TERMINAL DESIGNATIONS

ACB COOL

ACB HEAT

PARK

ACB LOW

ACC

TX

HOT

HTG ACC

NEUTRALS

24VAC HOT

24VAC RTN

FLAME SENSE

Blower − Cooling Speed (Line Volt)

Blower − Heating Speed (Line Volt)

Alternate Blower Speeds (Dead)

Continuous Low Speed Blower

Accessory Terminal (Line Volt)

120VAC Hot to Transformer

120VAC Hot Input

Heat Only Accessory (Line Volt)

120VAC Neutrals

24VAC Hot from Transformer

24VAC Return from Transformer

Flame Sense Terminal

B−Blower Motors and Capacitors

All 80MGF units use direct drive blower motors. All motors

used are 120V permanent split capacitor motors to ensure

maximum efficiency. See table 11 for ratings.

TABLE 1180MGF BLOWER RATINGS 120V 1PH

BLOWER MOTOR HP

80MGF2

80MGF3

80MGF3/4

CAP

1/2

1/3

1/4 5MFD 370V

5MFD 370V

7.5MFD 370V

80MGF5/6

80MGF4

80MGF4/5

1/2 7.5MFD 370V

3/4 40MFD 370V

3/4 40MFD 370V

FrontBottom

Right

Left

TopBack

FIGURE 13

SUPPLY AIR BLOWERAND SECONDARY LIMITS

BLOWERMOTOR

To Remove Blower From Unit: Remove Bolts andWiring Jackplugs. Then Slide Out Front of Unit.

MOTORCAPACITOR

SECONDARYLIMITS (S21)

C−Combustion Air Blower (B6)All 80MGF units use a combustion air blower to move air

through the burners and heat exchanger during heating

operation. The blowers will use either a shaded pole 120V

motor or a C−frame 120V motor. Shaded pole and C−frame

motors do not use run capacitors. The motor operates dur-

ing all heating operation and is controlled by furnace con-

trol A3. The motor also operates for a period before burner

ignition (pre−purge). The pre−purge time is 45 seconds for

80MGF units equipped with the RAM control and 15 sec-

onds for units equipped with the EGC control. With either

the RAM, EGC or SureLight control board, the motor will

operate 5 seconds after the gas valve closes (post-purge).

A pressure switch connected to the combustion air blower

housing is used to prove combustion air blower operation.

The switch monitors air pressure in the blower housing. Dur-

ing normal operation, the pressure in the housing is nega-

tive. If pressure becomes less negative (signifying an ob-

struction) the pressure switch opens. When the pressure

switch opens, the furnace control (A3) immediately closes

the gas valve to prevent burner operation.

D−Flame Rollout Switches (S47)Flame rollout switch is a high temperature limit located on

top of the burner box. Each furnace is equipped with two

identical switches. One switch is located over the leftmost

burner and the other switch is located over the rightmost

burner. The limit is a N.C. SPST manual-reset limit con-

nected in series with the ignition control A3. When S47

senses rollout, the ignition control immediately stops igni-

tion and closes the gas valve. If unit is running and flame

rollout is detected, the gas valve will close and ignition con-

trol will be disabled. Rollout can be caused by a blocked

flue or lack of combustion air. The switch is factory set and

cannot be adjusted. The setpoint will be printed on the side of

the limit. The switch can be manually reset. To manually re-

set a tripped switch, push the reset button located on the

control.

FIGURE 14

ROLLOUT SWITCH (S47)

MANUALRESET BUTTON

E−Primary Limit Control (S10)

FIGURE 15

80MGF SERIES UNITSLIMIT CONTROL FOR

THIS TYPE AUTO-RESET LIMITIS USED FOR THE PRIMARY LIMIT (S10) AND

RIGHT SECONDARY LIMIT (S21)(see FIGURE 13)

The primary limit (S10) on 80MGF units is located in the

middle of the heating vestibule panel. When excess heat is

sensed in the heat exchanger, the limit will open. If the limit is

tripped, the furnace control energizes the supply air blower

and closes the gas valve. The limit automatically resets when

unit temperature returns to normal. The switch is factory set

and cannot be adjusted. The switch may have a different

setpoint for each unit model number. However, the setpoint

will be printed on the side of the limit. There are two types of

primary limit. See figures 15 and 16.

F−Secondary Limit Controls (S21)The secondary limit (S21) on 80MGF units is located in the

blower compartment in the back side of the blower housing.

When excess heat is sensed in the heat blower compartment,

the limit will open. If the limit is tripped, the furnace control en-

ergizes the supply air blower and closes the gas valve. The

limit automatically resets when unit temperature returns to

normal. The switch is factory set and cannot be adjusted.

Two limits are supplied in each furnace and each limit is a

different style (figures 15 and 16). The setpoint will be

printed on the side of the limit. If stick limit (Figure 16) suf-

fers from nuisance trips and the furnace is in the horizontal

position, replace with limit kit no. 50L98.

INSULATING COVER (s)

FIGURE 16

LIMIT CONTROL (S21) (S10)FOR 80MGF SERIES UNITS

SPAD

E C

ON

NE

CT

OR

S

INSU

LA

TIN

G C

OV

ER L

IMIT

LIM

IT

THIS TYPE AUTO-RESET LIMIT ISUSED FOR THE LEFT SECONDARY

LIMIT (S21) (see FIGURE 13)

G−Spark Electrode and Flame Sensor(Models with EGC or Ram control only)

Figure 17 shows the arrangement of flame sensor, spark

electrode and burners. The Ram and EGC ignition control

uses direct spark to ignite the rightmost burner and the

burners cross-light to the left. The flame sensor uses flame

rectification to sense combustion. A flame retention ring in

the end of each burner is used to maintain correct flame

length and shape and to keep the flame from lifting off the

burner head.

Figure 18 shows the gap between tip of the electrodes and

the burner surface.

H−Gas ValveThe 80MGF uses a gas valve manufactured by Honey-

well or WhiteRodgers. The valve is internally redundant to

assure safety shut−off. If the gas valve must be replaced,

the same type valve must be used.

24VAC terminals and gas control knob are located on top of

the valve. All terminals on the gas valve are connected to

wires from the electronic ignition control. 24V applied to the

terminals energizes the valve.

Inlet and outlet pressure taps are located on the valve. A regu-

lator adjustment screw is located on the valve. Refer to figures

19 or 20 for location of valve features.

An LPG changeover kit is available from Lennox. The kit in-

cludes burner orifices and a regulator conversion kit.

FIGURE 17

TYPICAL BURNER/ELECTRODE ORIENTATIONDIRECT SPARK MODELS ONLY

BURNER

FLAME RETENTION RING

UPPER BURNERMOUNTING RAIL

LOWER BURNERMOUNTING RAIL

MANIFOLD ORIFICE

Right Left

Top

Bottom

FLAME SENSORSPARK ELECTRODE GROUND

1/8"(+1/64")

23/32 in.(18 mm)

FIGURE 18

SPARK ELECTRODE TO BURNER GAP

SPARK ELECTRODE

BURNER

FLAME SENSOR TO BURNER GAPBURNER

FLAME SENSOR

SPARKELECTRODE

5/16 in.(7 mm)

5/16 in.(7 mm)

FIGURE 19

WHITE RODGERS 36E SERIES GAS VALVE

GAS VALVE SHOWN IN OFF POSITION

MANIFOLDPRESSURE

ADJUSTMENTSCREW

MANIFOLDPRESSURE

OUTLET

ON

OFF

FIGURE 20

HONEYWELL VR8205 SERIES GAS VALVE

GAS VALVE SHOWN IN OFF POSITION

MANIFOLDPRESSURE

ADJUSTMENTSCREW

MANIFOLDPRESSURE

OUTLET

I−Combustion Air Blower Prove (Pressure) Switch (S64)

80MGF series units are equipped with a combustion airprove switch located on the vestibule panel. The switch isconnected to the combustion air blower housing by meansof a flexible silicone hose. It monitors air pressure in thecombustion air blower housing.

The switch is a single-pole single-throw pressure switch

electrically connected to the furnace control. The purpose

of the switch is to prevent burner operation if the combus-

tion air blower is not operating.

FIGURE 21

PROVE SWITCHCOMBUSTION AIR BLOWER

PROVE SWITCHNormally Open

Closes on Negative Pressure

PROVESWITCH

Sensing TubeAttaches to TopSide Of Blower

Top

Bottom

Left

RightBack

Front

On start-up, the switch senses that the combustion airblower is operating. It closes a circuit to the furnace controlwhen pressure inside the combustion air blower increasesabove pressure switch set point (In. negative w.c.). Thepressure sensed by the switch is relative to atmosphericpressure. If the flue becomes obstructed during operation,the switch senses a loss of negative pressure (pressurebecomes more equal with atmospheric pressure) andopens the circuit to the furnace control and gas valve. Theswitch trip pressure is different depending on unit modelnumber. The trip pressure is printed on the side of the limit.

The switch is factory set and is not field adjustable. It is a

safety shut-down control in the furnace and must not be

bypassed for any reason.

II−PLACEMENT AND INSTALLATION

Make sure unit is installed in accordance with installation

instructions and applicable does.

III−START-UP

BEFORE LIGHTING smell all around the appliance area

for gas. Be sure to smell next to the floor because some gas

is heavier than air and will settle on the floor.

Use only your hand to turn the gas control knob. Never use

tools. If the knob will not turn by hand, do not try to repair it,

call a qualified service technician. Force or attempted repair

may result in a fire or explosion.

A−Preliminary and Seasonal Checks1− Inspect electrical wiring, both field and factory installed

for loose connections. Tighten as required.

2− Check voltage at disconnect switch. Voltage must be

within range listed on the nameplate. If not, consult the

power company and have voltage condition corrected

before starting unit.

B−Heating Start-Up

1 − STOP! Read the safety information at the beginning

of this section.

2 − Set thermostat to lowest setting.

3 − Turn off all electrical power to appliance.

4 − This appliance is equipped with an ignition device

which automatically lights the burners. Do not try to

light the burners by hand.

5 − Remove access panel.

WARNINGShock and burn hazard.

80MGF units are equipped with a direct spark igni-tion system. Do not attempt to light manually.

6 − White Rodgers 36E Gas Valve −− Switch gas valve

lever to OFF. See figure 19.

Honeywell VR8205 Gas Valve −− Turn knob on gas

valve clockwise to OFF. Do not force. See fig-

ure 20.

7 − Wait five (5) minutes to clear out any gas. If you then

smell gas, STOP! Immediately call your gas supplier

from a neighbor’s phone. Follow the gas supplier’s in-

structions. If you do not smell gas go to next step.

8 − White Rodgers 36E Gas Valve −− Switch gas valve lever

to ON.

Honeywell VR8205 Gas Valve −− Turn knob on gas

valve counterclockwise to ON. Do not force.

9 − Replace access panel.

10− Turn on all electrical power to unit.

11− Set thermostat to desired setting.

12− If the appliance will not operate, follow the instructions

�To Turn Off Gas To Unit" and call your service techni-

cian or gas supplier.

Turning Off Gas To Unit

1 − Set thermostat to lowest setting.

2 − Turn off all electrical power to unit if service is to be

performed.

3 − Remove access panel.

4 − Switch lever on White Rodgers gas valve to OFF; turn

knob on Honeywell valve clockwise to OFF. Do not

force.

5 − Replace lower access panel.

C−Safety or Emergency Shutdown

Turn off unit power. Close manual and main gas valves.

D−Extended Period Shutdown

Turn off thermostat or set to �UNOCCUPIED" mode. Close

all gas valves (both internal and external to unit) to guaran-

tee no gas leak into combustion chamber. Turn off power

to unit. All access panels, covers and vent caps must be in

place and secured.

IV−HEATING SYSTEM SERVICE CHECKS

A−A.G.A./C.G.A. Certification

All units are A.G.A. and or C.G.A. design certified without

modifications. Refer to the 80MGF Operation and Installa-

tion Instruction Manual Information.

B−Gas Piping

Gas supply piping should not allow more than 0.5"W.C.

drop in pressure between gas meter and unit. Supply gas

pipe must not be smaller than unit gas connection.

Compounds used on gas piping threaded joints should be

resistant to action of liquefied petroleum gases.

C−Testing Gas Piping

IMPORTANTIn case emergency shutdown is required, turn offthe main shut-off valve and disconnect the mainpower to unit. These controls should be properlylabeled by the installer.

When pressure testing gas lines, the gas valve must be

disconnected and isolated. Gas valves can be damaged if

subjected to more than 0.5psig (14" W.C.). See figure 22. If

the pressure is equal to or less than 0.5psig (14"W.C.), use

the manual shut−off valve before pressure testing to iso-

late furnace from gas supply.

FIGURE 22

MANUAL MAIN SHUT−OFF VALVE

WILL NOT HOLD TEST PRESSUREIN EXCESS OF 0.5 PSIG (14"W.C.)

GAS VALVECAP

GAS PIPING TEST PROCEDURE

FIELD PROVIDEDLINE PRESSURE TAP

When checking piping connections for gas leaks, use pre-

ferred means. Kitchen detergents can cause harmful corro-

sion on various metals used in gas piping. Use of a specialty

Gas Leak Detector is strongly recommended. It is available

through Lennox under part number 31B2001. See Corp.

8411−L10, for further details.

Do not use matches, candles, flame or any other source of

ignition to check for gas leaks.

D−Testing Gas Supply PressureWhen testing supply gas pressure, connect test gauge to

inlet pressure tap (field provided). See figure 22. Check

gas line pressure with unit firing at maximum rate. Low

pressure may result in erratic operation or underfire. High

pressure can result in permanent damage to gas valve or

overfire. For natural gas units, operating pressure at unit

gas connection must be a minimum of 4.5" W.C. For L.P.

gas units, operating pressure at unit gas connection must

be a minimum of 9.0" W.C.

On multiple unit installations, each unit should be checked

separately, with and without other units operating. Supply

pressure must fall within range listed in previous para-

graph.

E−Check Manifold PressureAfter line pressure has been checked and adjusted, check

manifold pressure. Move pressure gauge to outlet pres-

sure tap located on unit gas valve (GV1). Checks of man-

ifold pressure are made as verification of proper regulator

adjustment. Manifold pressure for the 80MGF can be mea-

sured at any time the gas valve is open and is supplying gas

to the unit. Normal manifold pressure for natural gas units is

3.5 in. w.c. For LP/propane gas the correct manifold pres-

sure is 9.0 in. w.c.

IMPORTANTFor safety, connect a shut-off valve between themanometer and the gas tap to permit shut off ofgas pressure to the manometer.

Operating Pressure (outlet) in. W.C.

TABLE 12GAS VALVE REGULATION

3.5 +0 −0.3Natural

L.P. 9.0 + 0.5

Unit (Fuel)

The gas valve is factory set and should not require adjust-

ment. All gas valves are factory regulated. See table 12.

Manifold Adjustment Procedure:

1− Connect a test gauge to outlet pressure tap on gas

valve. Start unit and allow 5 minutes for unit to reach

steady state.

2− While waiting for the unit to stabilize, notice the flame.

Flame should be stable and should not lift from burner.

Natural gas should burn blue. L.P. gas should burn

mostly blue with some orange streaks.

3− After allowing unit to stabilize for 5 minutes, record

manifold pressure and compare to values given in

table 12.

NOTE−Shut unit off and remove manometer as soon as

an accurate reading has been obtained. Take care to

replace pressure tap plug.

F− Proper Gas Flow (Approximate)Furnace should operate at least 5 minutes before check-

ing gas flow. Determine time in seconds for two revolu-

tions of gas through the meter. (Two revolutions assures

a more accurate time.) Divide by two and compare to

time in table 13 below. Adjust manifold pressure on gas

valve to match time needed.

NOTE− To obtain accurate reading, shut off all othergas appliances connected to meter.

TABLE 13

GAS METER CLOCKING CHART

Seconds for One Revolution

80mgf Natural LPgUnit 1 cu ft

Dial2 cu ftDial

1 cu ftDial

2 cu ftDIAL

−45 80 160 200 400

−60 60 120 150 300

−75 48 96 120 240

−100 36 72 90 180

−120 30 60 75 150

−140 25 50 64 128

Natural−1000 btu/cu ft LP−2500 btu/cu ft

G−High Altitude DerateNOTE−In Canada, certification for installation at alti-

tudes over 4500 ft. (1372m) above sea level is the juris-

diction of the local authorities.

80MGF−1 through −8 Models

This unit does not require gas pressure adjustment, or

pressure switch change when operating at elevations of 0

to 7500 ft. (0 to 2248m). Check gas line pressure with unit

firing. The minimum pressure as shown on the nameplate

for natural and propane gases must be maintained. No ori-

fice change is required.

NOTE−This is the only permissible field derate for this

appliance.

80MGF−9, −10 and −11 Models

Table 14 shows manifold pressure settings for installations

at different altitudes. Refer to table 15 for pressure switch

replacement for models at elevations of 4500 feet (1372m)

and greater.

TABLE 14

ALTITUDEfeet (m)

GAS FUELMANIFOLDPRESSURE

in. W.C. (kPa)

0 − 4500 Natural 3.5 (0.87)0 4500(0 − 1372) Propane/LP 9.5 (2.36)




TABLE 15

Unit Model Pressure Switch Part Number

80MGF−45 No Change


80MGF−75 88J8001

80MGF−100 18L2401

80MGF−120 18L2401


H−Flame Signal

A microamp DC meter is needed to check the flame signal

on the primary ignition control.

Flame (microamp) signal is an electrical current which

passes from the furnace control through the sensor elec-

trode during unit operation. Current passes from the sen-

sor through the flame to ground to complete a safety cir-

cuit.

To Measure Flame Signal:

1− Place meter in series between furnace control and

sensor wire. Connect the positive (+) lead of meter to

the ignition control sensor connection and the nega-

tive (−) lead of the meter to the sensor wire. See figure

23.

2− Set thermostat for a heating demand and check flame

signal with unit operating. See table 16 for microamp

reading for the various control boards used.

FLAME SIGNAL TEST

FIGURE 23

IGNITIONCON-TROL

�SENSE"TERMINAL

SENSORWIRE

D.C. MICROAMPMETER

FLAMESENSOR

TABLE 16

CONTROLMICROAMP

SIGNALDROP OUT

SIGNAL

Ram 1.0 to 5.0 �1.0

EGC 1.0 to 5.0 �.45

SureLight �.70 �.15

Flame signal may rise above 5 microamps for the first few

seconds after ignition then level off within the range.

WARNINGFire and explosion hazard.These instructions MUST be followed exactly.Can cause a fire or explosion resulting in propertydamage, personal injury or loss of life.

V−TYPICAL OPERATING CHARACTERISTICS

A−Blower Operation and Adjustment

NOTE− The following is a generalized procedure and

does not apply to all thermostat controls.

1− Blower operation is dependent on thermostat control

system.

2− Generally, blower operation is set at thermostat sub-

base fan switch. With fan switch in ON position, blower

operates continuously on heating speed. With fan

switch in AUTO position, blower cycles with demand or

runs continuously while heating or cooling circuit cycles.

3− Depending on the type of indoor thermostat, blower

and entire unit will be off when the system switch is in

OFF position.

B−Temperature RiseTemperature rise for 80MGF units depends on unit input,

blower speed, blower horsepower and static pressure as

marked on the unit rating plate. The blower speed must be

set for unit operation within the range of �AIR TEMP. RISE

°F" listed on the unit rating plate.

FIGURE 24

STATIC PRESSURETEST

MANOMETER

80MGF UNIT

To Measure Temperature Rise:

1 − Place plenum thermometers in the supply and return

air plenums. Locate supply air thermometer in the first

horizontal run of the plenum where it will not pick up ra-

diant heat from the heat exchanger.

2 − Set thermostat to highest setting.

3 − After plenum thermometers have reached their high-

est and steadiest readings, subtract the two readings.

The difference should be in the range listed on the unit

rating plate. If the temperature is too low, decrease

blower speed. If temperature is too high, first check

the firing rate. Provided the firing rate is acceptable, in-

crease blower speed to reduce temperature. To

change blower speed taps see the Blower Speed Taps

section in this manual.

C−External Static Pressure

1 − Measure tap locations as shown in figure 24.

2 − Punch a 1/4" diameter hole

in supply and return air ple-

nums. Insert manometer

hose flush with inside edge

of hole or insulation. Seal

around the hose with per-

magum. Connect the zero

end of the manometer to the

discharge (supply) side of the system. On ducted sys-

tems, connect the other end of manometer to the re-

turn duct as above. For systems with non−ducted re-

turns, leave the other end of the manometer open to

the atmosphere.

3 − With only the blower motor running and the evaporator

coil dry, observe the manometer reading. Adjust blow-

er motor speed to deliver the air desired according to

the job requirements.

4 − External static pressure drop must not be more than

0.5" W.C.

5 − Seal around the hole when the check is complete.

D−Blower Speed Taps Leadless Motors

Blower speed tap selection is accomplished by changing the

taps at the blower motor harness connector. Disconnect har-

ness connector from motor to expose speed selectors.

Blower speed selections are listed in table 17.

To Change Blower Speed:

1 − Turn off electric power to furnace.

2 − Remove front panel and blower access door. See

figure 4.

3 − Disconnect blower motor harness from motor.

4 − Select desired speeds for heating and cooling. (Red =

heating, Black = cooling, White = common). See table

17.

TABLE 17

BLOWER SPEED SELECTION

Unit

Factory ConnectedSpeed Taps Speeds

AvailableUnit

Cool (Black) Heat (Red)Available

80MGF2-45 2 4 4

80MGF2-60 2 4 4

80MGF3-60 2 4 4

80MGF2-75 2 3 4

80MGF3-75 2 4 4

80MGF4-75 2 4 5

80MGF3/4-100 2 4 5

80MGF4/5-100 2 5 5

80MGF3/4-120 2 3 5

80MGF4/5-120 2 5 5

80MGF4/5-140 2 3 5

BLOWER SPEED SELECTIONHI LOW

2 3 4 5

2 3 4 5 6

4

5

◊

◊◊

MOTOR PLUG SPEED TAP DESIGNATION

2 3 4◊ 3

TABLE 18

TAPS AVAILABLE

5 − Depress harness connector tab to release wire termi-

nal. Select connector location for new speed (refer to

unit wiring diagram). Insert wire terminal until it is se-

curely in place. See figure 25.

6 − Replace harness connector to motor.

BLOWER SPEED TAP SELEC-TION

Leadless motors only

FIGURE 25

HARNESSCONNECTOR

MOTOR

DEPRESS TAB TO RELEASEWIRE TERMINAL. SELECTCONNECTOR LOCATION FORNEW SPEED (REFER TO UNITWIRING DIAGRAM). INSERTWIRE UNTIL IT IS SECURELYIN PLACE.

E−Blower Speed Taps Leaded Motors

−11 Models

Blower speed tap changes are made on the SureLightcontrol board. See figure 8. Unused taps must be securedon dummy terminals "PARK M1" and or "PARK M2" on theSureLight board. The heating tap is connected to the "ACBHEAT " terminal and the cooling tap is connected to the"ACB COOL" terminal. The continuous blower tap is con-nected to the "ACB LOW" terminal.To change existing heat tap, turn off power then switch out

speed tap on "ACB HEAT" with tap connected to "PARK

M1" or "PARK M2". See table 19 for blower motor tap col-

ors for each speed.

TABLE 19

VI−MAINTENANCE

At the beginning of each heating season, the systemshould be checked as follows:

Filters

All 80MGF filters are installed external to the unit. Filtersshould be inspected monthly and cleaned or replacedwhen necessary to assure proper furnace operation. Seetable 20 for filter sizes. Replacement filters for80MGF-45/60/75 units must have a minimum velocity rat-ing of 400 FPM. Replacement filters for80MGF-100/120/140 units require a minimum velocity rat-ing of 625 FPM.

TABLE 20

MODEL NUMBER FILTER SIZE

80MGF−45/60/75 16" X 20" X 1"

80MGF−100/120/140 20" X 20" X 1"

WARNINGBlower door must be securely in place when blow-er and burners are operating. Gas fumes, whichcould contain carbon monoxide, can be drawninto living space resulting in personal injury ordeath.

A−Cleaning Heat Exchanger and Burners

NOTE−Use papers or protective covering in front of fur-

nace while cleaning furnace.

Due to dimples designed in the heatexchanger, cleaning is

not recommended. Removal is for inspection only.

Burners

Burners and burner flame should be inspected at the be-ginning of each heating season. Clean burners, if neces-sary, as outlined below:

1 − Turn off electrical and gas supply to unit.

2 − Remove burner box top.

3 − Remove burner retaining bracket.

4 − Remove burners.

5 − Clean burner insert with bottle brush as shown in fig-

ure 26.

NOTE−Use papers or protective covering in front of fur-

nace while cleaning furnace.

FIGURE 26

CLEANING BURNERS

BOTTLEBRUSH

BURNER

6 − Use bottle brush to clean inside of each burner.

7 − Replace burners and burner retaining bracket, mak-ing sure burners are properly seated in slots on trayand orifice in manifold.

8 − Check electrode gap using appropriately sized twist

drills or feeler gauges. Gap should be between 2.79 to

3.56mm (0.110 and 0.140 inches).

9 − Reinstall burner box top.

CAUTIONSome soaps used for leak detection are corrosiveto certain metals. Carefully rinse piping thorough-ly after leak test has been completed. Do not usematches, candles, flame or other sources of igni-tion to check for gas leaks.

10 − Restore electrical power and gas supply. Follow light-ing instructions on front of unit. Check the following:

appearance of burner flame, burner pressure, gas flowand temperature rise. Make adjustments, if necessary.See adjustments section.

B−Supply Air Blower1 − Check and clean blower wheel.

2 − Motors used on the Lennox 80MGF series units arepermanently lubricated and need no further lu-brication.

C−Flue and Chimney

Flue must conform to all AGA/GAMA venting require-

ments. Flue pipe deteriorates from the inside out and must

be disconnected in order to check thoroughly. Check flue

pipe, chimney and all connections for tightness and to

make sure there is no blockage or leaks.

D−Electrical

1 − Check all wiring for loose connections.

2 − Check for correct voltage.

3 − Check amp−draw on blower motor.

CAUTIONPotential for gas leaks, fire or explosion.Some soaps used for leak detection are corrosiveto certain metals. Carefully clean piping thor-oughly after leak detection has been completed.Can cause damage to piping resulting in gasleaks, fire or explosion.

FIGURE 27

HEAT EXCHANGER REMOVAL (unit shown in horizontal position)

REMOVE SCREWS (4)

SLIDE ENTIRE ASSEMBLY OUT OF CABINET

Front

Right

TopBottom

Left

Back

VII−WIRING AND SEQUENCE OF OPERATION

2 3

5

6

8

74

1

80MGF WITH RAM CONTROL

1- When disconnect is closed, 120V is routed throughdoor interlock switch (S51) to feed the line voltageside of the furnace control (A3) and transformer T1 pri-mary. Door interlock switch must be closed for A3 andT1 to receive voltage.

2- T1 supplies 24VAC to terminal �24VAC" on A3. In turn,terminal �R" of A3 supplies 24VAC to terminal �RC" ofthe indoor thermostat (not shown).

3- When there is a call for heat, W1 of the thermostat en-ergizes W of the furnace control with 24VAC.

4- CMB BLWR of the blower control energizes the com-bustion air blower (B6). When the combustion airblower nears full speed, combustion air prove switch(S18) closes.

5- When S18 closes, assuming the flame rollout switch(S47) primary limit (S10) and secondary limits (S21)are closed, the furnace control begins a 45 secondtime-delay (pre-purge).

6- At the end of the pre-purge cycle, the furnace controlsimultaneously opens the gas valve and sends highvoltage to the spark electrode.

7- When flame is sensed, the furnace control begins a 45second delay before energizing the indoor blower.

8- When heat demand is satisfied, W1 of the thermostatde-energizes W of the furnace control and the furnacecontrol immediately de-energizes the gas valve. Thecombustion air blower runs for 5 seconds (post-purge)before being de-energized. Also, the indoor blowerruns for a designated period (90−240 seconds) as setby switches on furnace control.

80MGF TROUBLESHOOTING SEQUENCE

NORMAL HEATING MODE ABNORMAL HEATING MODE

LED: SLOW FLASH RATE

THERMOSTAT CALLS FOR HEAT

LED: FAST FLASH RATE

FLAME OFF?

CONTROL SELF−CHECK OKAY?

HI LIMIT SWITCH CLOSED?

PRESSURE SWITCH OPEN?

COMBUSTION AIR BLOWER ON?

PRESSURE SWITCH CLOSED?

PREPURGE (45 seconds)

IGNITION TRIAL (7 seconds) −− START IGNITIONSPARK, OPEN MAIN GAS VALVE. INCREMENT

TRIAL REGISTER. HAS FLAME BEENREGISTERED WITHIN 7 SECONDS?

SYSTEM FAN ON. (Fixed 45−second delay)

FLAME SENSE OKAY?

FLAME CONTINUOUSLY CHECKED?

ROLLOUT SWITCHES CLOSED

HI LIMIT SWITCH CLOSED?

PRESSURE SWITCH CLOSED?

THERMOSTAT OPENS


COMB. AIR BLOWER OFF (5 sec. delay)

FAN OFF (After selected 90, 120,180, or 240 delay)?

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

LOCKOUT: MAIN VALVE OFFCOMB. AIR AND SYSTEM FANS ON

RESET THERMOSTATLED: 5 flash if flame sensed with valve off

LED: Steady on if control board failure

NO

NO

CHECK TO SEE IF MAIN VALVE IS OFF.SEQUENCE HOLDS UNTIL HI LIMIT CLOSES.

LED: 4 flashes.

NO

CHECK TO SEE IF MAIN VALVE IS OFF.SEQUENCE HOLDS UNTIL PRES. SWITCH OPENS.

LED: 3 flashes.

CHECK TO SEE IF MAIN VALVE IS OFF.SEQUENCE HOLDS UNTIL PRES. SWITCH CLOSES.

LED: Fast flash rate.

MAIN VALVE AND SPARK ARE OFF.INCREMENT TRIAL REGISTERTHREE TRIALS COMPLETED?

NO

NO

NO

IGNITION RESET PERIODCOMBUSTION & SYSTEM FANS OFF.

IS 60 MIN. RESET PERIOD COMPLETE?LED: Fast flash rate.

MAIN VALVE AND SPARK OFF.

START IGNITION SPARK (IN 0.8 SEC. MAXIMUM).HAS FLAME BEEN DETECTED WITHIN 7 SEC.?

SEQUENCE HOLDS. MAIN VALVE OFF.COMBUSTION AND SYSTEM FANS ON.

RESET OR REPLACE ROLLOUT SWITCH.LED: 4 flashes.

MAIN VALVE OFF. COMBUSTION & SYSTEM FANS ON.SEQUENCE HOLDS UNTIL SWITCH CLOSES.

LED: 4 flashes for hi limit.LED: 3 flashes for pressure switch.

SWITCH CLOSED

COMBUSTION FAN ON. SYSTEM FAN OFF.(AFTER DELAY TO OFF INTERVAL COMPLETED.)

LED: Fast flash rate.

NO

YES

YES

NO

NO

YES

NO

NO

NO

YES

80MGF TROUBLESHOOTING SEQUENCE − COOLING

YES

THERMOSTAT CALLS FOR COOLING.

LED: Slow flash rate.REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.

NO

COMPRESSOR CONTACTOR AND SYSTEM FANENERGIZED AT COOLING SPEED AFTER

1 SECOND DELAY.

THERMOSTAT OPENS.

COMPRESSOR OFF.

SYSTEM FAN OFF AFTER COMPLETINGSELECTED DELAY INTERVAL

(At dip switches).

80MGF TROUBLESHOOTING SEQUENCE − FAN ONLY

MANUAL FAN SELECTION MADE AT THERMOSTAT.CONTROL ENERGIZES SYSTEM FAN

AT HEATING SPEED.

THERMOSTAT CALLS FOR HEAT.

LED: Slow flash rate.REMAINS UNCHANGED THROUGHOUT SEQUENCE.

THERMOSTAT CALLS FOR COOLING.SYSTEM FAN REMAINS ON HEATING SEQUENCE AND

RUNS THROUGH COMPLETION.

SYSTEM FAN SWITCHEDTO COOLING SPEED. COOLING

SEQUENCE RUNS TO COMPLETION.

SYSTEM FAN ON AT HEATING SPEEDUNTIL MANUAL FAN IS SWITCHED

OFF AT THERMOSTAT.

YES NO

LED CODES

SLOW FLASH

FAST FLASH

2 FLASH

3 FLASH

4 FLASH

5 FLASH

STEADY ON

NORMAL OPERATION. NO CALL FOR HEAT.

NORMAL OPERATION. CALL FOR HEAT.

SYSTEM LOCKOUT. FAILURE TO DETECT OR SUSTAIN FLAME.

PRESSURE SWITCH OPEN OR CLOSED.

HIGH LIMIT OR ROLLOUT SWITCH OPEN.

FLAME SENSED AND GAS VALVE NOT ENERGIZED.

CONTROL BOARD FAILURE.

.

80MGF WITH EGC−2 IGNITION CONTROL1 − When disconnect is closed, 120V is routed through door

interlock switch (S51) to feed the line voltage side of theignition control (A3) and transformer T1 primary. Door in-terlock switch must be closed for A3 and T1 to receivevoltage.

2 − T1 supplies 24VAC to terminal �24VAC" on A3. In turn,terminal �R" of A3 supplies 24VAC to terminal �R" of theindoor thermostat (not shown).

3 − When there is a call for heat, W1 of the thermostat en-ergizes W of the ignition control with 24VAC.

4 − CAB of the ignition control energizes the combustion airblower (B6). When the combustion air blower nearsfull speed, combustion air prove switch (S18)closes.

5 − When S18 closes, assuming primary limit (S10) and

secondary limit (S21) are closed, a 15 second pre−purge

begins. After the pre−purge period the ignition control

starts ignition spark and opens main gas valve.

6 − After 45 seconds, ignition control (A3) energizes the

indoor blower (B3).

7 − When heat demand is satisfied, W1 of the thermostat de-

energizes W of the ignition control and the gas valve is

immediately de-energized. The combustion air blower

immediately stops. The indoor blower runs for a desig-

nated fan �off" period (60−240 seconds) as set by jumper

on ignition control.

80MGF WITH EGC−2 HEATING SEQUENCE OF OPERATION





FLAME OFF?


COMB. AIR BLOWER PRESSURE SWITCH OPEN?

PRESSURE SWITCH CLOSED WITHIN 2.5 MIN.?

COMB. AIR BLOWER PREPURGE (15 seconds)

HAS FLAME REGISTERED WITHIN 10 SECONDSAFTER IGNITION TRIAL?

YES

YES

YES

YES

NO

CONTROL MAIN POWER �ON"

ROLL−OUT SWITCH CLOSED

YES

GAS VALVE OFF. COMB. BLOWER ON. INDOORBLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL

NO FLAME SENSED OR MAIN POWER IS INTERRUPTEDAND RESET. DIAG. CODE: 1− FLASHING; 2−OFF(FLAME SENSED WITHOUT VALVE ENERGIZED)

GAS VALVE, COMB. BLOWER AND INDOOR BLOWER(WITH DELAY) OFF. REMOVE POWER TO RESET

CONTROL. DIAG. CODE: BOTH ON (CONTROLSELF−CHECK FAILURE OR INCORRECT WIRING)

GAS VALVE, COMB. BLOWER AND INDOOR BLOWER(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL

ROLL−OUT SWITCH IS MANUALLY CLOSED.DIAG. CODE: 1−ON;

2−FLASHING (FLAME ROLL−OUT OPEN)


PRESSURE SWITCH CLOSES OR THERMOSTATRESETS CONTROL. DIAG. CODE: 1−OFF;

2−FLASHING (C.A.B. PRESSURE SWITCH OPEN)

COMBUSTION AIR BLOWER ON?HTG ACC. TERM. ENERGIZED.

PRESSURE SWITCH WATCHGUARD CONDITION:GAS VALVE, COMB. BLOWER AND INDOOR BLOWER

(WITH DELAY) OFF. DIAG. CODE: 1−OFF /2−FLASHING (C.A.B. PRESSURE SWITCH OPEN) IS 5

MINUTE RESET PERIOD COMPLETE?

INDOOR AIR BLOWER ON. (Fixed 45−second delay)

PRIMARY/SECONDARY LIMITS MONITORED INHEAT CYCLE. ARE SWITCHES CLOSED?

YESNO

GAS VALVE OFF. COMB. BLOWER OFF. INDOORBLOWER ON UNTIL LIMIT CLOSES. DIAG.CODE: 1−FLASHING / 2−ON (LIMIT OPEN)

IS LIMIT NOW CLOSED?PRESSURE SWITCH CLOSED?

YES

HAS PRIMARY LIMIT OPENED 5 TIMES DURINGONE UNSATISFIED HEAT DEMAND. IF YES,

SYSTEM GOES INTO 60 MIN.WATCHGUARD.DIAG. CODE: 1−FLASHING / 2−ON

IF NO, GO TO �COMB. AIR BLOWER ON?"

THERMOSTAT OPENS


COMB. AIR BLOWER OFF (5 sec. delay)HTG ACC. TERM.DE−ENERGIZED.

INDOOR AIR BLOWER OFF (After selected 60, 90,120, 180, or 240 delay)?

GAS VALVE, COMB. BLOWER AND INDOOR BLOWER(WITH DELAY) OFF. DIAG. CODE: 1−OFF / 2−FLASHING

(C.A.B. PRESSURE SWITCH OPEN) HAS C.A.B.PRESSURE SWITCH CLOSED IN 2.5 MINUTES?

NO

NO

NO

NO

NO

YES

NO

GAS VALVE OFF. COMB. BLOWER ON. INDOORBLOWER (WITH 45 DELAY) ON. HAS CONTROL FAILEDFLAME SENSE 5 TIMES DURING ONE HEAT DEMAND?IF YES, SYSTEM GOES INTO 60 MIN.WATCHGUARD.DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF

NO, GO TO �COMB. AIR BLOWER ON?"IS FLAME SENSED AFTER 10 SECOND

FLAME RECTIFICATION PERIOD?

NO

NO

HAS CONTROL RESET IGNITION SEQUENCE 5 TIMESIF YES, SYSTEM GOES INTO 60 MIN. WATCHGUARD.DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF

NO, GO TO �COMB. AIR BLOWER ON?"

YES

YES

YES

YES

IGNITION TRIAL (10 seconds) −− START IGNITIONSPARK, OPEN MAIN GAS VALVE.

YES

80MGF WITH EGC−2 COOLING SEQUENCE OF OPERATION

YES



NO


1 SECOND DELAY. ACC TERMINAL ENERGIZED.

THERMOSTAT OPENS.

COMPRESSOR OFF.

SYSTEM FAN AND ACC TERMINAL OFF AFTER 0 SECONDS.

80MGF WITH EGC−2 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION

CONTINUOUS FAN SELECTION MADE AT THERMOSTAT.CONTROL ENERGIZES SYSTEM FAN AT HEAT SPEED.

ACC TERMINAL ENERGIZED.



THERMOSTAT CALLS FOR COOLING.SYSTEM FAN REMAINS ON HEATING SPEED AFTER

SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.

SYSTEM FAN SWITCHED TO COOLING SPEED. ACC TERMINAL REMAINS ENERGIZED.

SYSTEM FAN SWITCHES TO CONTINUOUS SPEEDAND ENERGIZES ACC TERMINAL. BOTH REMAIN ON

UNTIL CONTINUOUS FAN IS SWITCHED OFF AT THERMOSTAT.

YES NO

THERMOSTAT OPENS.

THERMOSTAT OPENS.

SYSTEM FAN SWITCHED OFF AFTER DELAY.ACC TERMINAL DE−ENERGIZED.

HTG ACC. TERM. ENERGIZED WITH COMB. AIR BLOWER.

80MGF WITH EGC−1 IGNITION CONTROL1 − When disconnect is closed, 120V is routed through door

interlock switch (S51) to feed the line voltage side of theignition control (A3) and transformer T1 primary. Door in-terlock switch must be closed for A3 and T1 to receivevoltage.

2 − T1 supplies 24VAC to terminal �24VAC" on A3. In turn,terminal �R" of A3 supplies 24VAC to terminal �R" of theindoor thermostat (not shown).

3 − When there is a call for heat, W1 of the thermostat en-ergizes W of the ignition control with 24VAC.

4 − CAB of the ignition control energizes the combustion airblower (B6). When the combustion air blower nearsfull speed, combustion air prove switch (S18)closes.

5 − When S18 closes, assuming primary limit (S10) and

secondary limit (S21) are closed, a 15 second pre−purge

begins. After the pre−purge period the ignition control

starts ignition spark and opens main gas valve.

6 − After 45 seconds, ignition control (A3) energizes the

indoor blower (B3).

7 − When heat demand is satisfied, W1 of the thermostat de-

energizes W of the ignition control and the gas valve is

immediately de-energized. The combustion air blower

immediately stops. The indoor blower runs for a desig-

nated fan �off" period (60−240 seconds) as set by jumper

on ignition control.

80MGF WITH EGC−1 HEATING SEQUENCE OF OPERATION





FLAME OFF?


COMB. AIR BLOWER PRESSURE SWITCH OPEN?

PRESSURE SWITCH CLOSED WITHIN 2.5 MIN.?

COMB. AIR BLOWER PREPURGE (15 seconds)

HAS FLAME REGISTERED WITHIN 10 SECONDSAFTER IGNITION TRIAL?

YES

YES

YES

YES

NO

CONTROL MAIN POWER �ON"

ROLL−OUT SWITCH CLOSED

YES

GAS VALVE OFF. COMB. BLOWER ON. INDOORBLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL

NO FLAME SENSED OR MAIN POWER IS INTERRUPTEDAND RESET. DIAG. CODE: 1− FLASHING; 2−OFF(FLAME SENSED WITHOUT VALVE ENERGIZED)

GAS VALVE, COMB. BLOWER AND INDOOR BLOWER(WITH DELAY) OFF. REMOVE POWER TO RESET

CONTROL. DIAG. CODE: BOTH ON (CONTROLSELF−CHECK FAILURE OR INCORRECT WIRING)


ROLL−OUT SWITCH IS MANUALLY CLOSED.DIAG. CODE: 1−ON;

2−FLASHING (FLAME ROLL−OUT OPEN)


PRESSURE SWITCH CLOSES OR THERMOSTATRESETS CONTROL. DIAG. CODE: 1−OFF;

2−FLASHING (C.A.B. PRESSURE SWITCH OPEN)

COMBUSTION AIR BLOWER ON?HTG ACC. TERM. ENERGIZED?

PRESSURE SWITCH WATCHGUARD CONDITION:GAS VALVE, COMB. BLOWER AND INDOOR BLOWER

(WITH DELAY) OFF. DIAG. CODE: 1−OFF /2−FLASHING (C.A.B. PRESSURE SWITCH OPEN) IS 5

MINUTE RESET PERIOD COMPLETE?

INDOOR AIR BLOWER ON. (Fixed 45−second delay)

PRIMARY/SECONDARY LIMITS MONITORED INHEAT CYCLE. ARE SWITCHES CLOSED?

YESNO

GAS VALVE OFF. COMB. BLOWER OFF. INDOORBLOWER ON UNTIL LIMIT CLOSES. DIAG.CODE: 1−FLASHING / 2−ON (LIMIT OPEN)

IS LIMIT NOW CLOSED?PRESSURE SWITCH CLOSED?

YES

HAS PRIMARY LIMIT OPENED 5 TIMES DURINGONE UNSATISFIED HEAT DEMAND. IF YES,

SYSTEM GOES INTO 60 MIN.WATCHGUARD.DIAG. CODE: 1−FLASHING / 2−ON

IF NO, GO TO �COMB. AIR BLOWER ON?"

THERMOSTAT OPENS


COMB. AIR BLOWER OFF (5 sec. delay)HTG ACC. TERM. DE−ENERGIZED.

INDOOR AIR BLOWER OFF (After selected 60, 90,120, 180, or 240 delay)?

GAS VALVE, COMB. BLOWER AND INDOOR BLOWER(WITH DELAY) OFF. DIAG. CODE: 1−OFF / 2−FLASHING

(C.A.B. PRESSURE SWITCH OPEN) HAS C.A.B.PRESSURE SWITCH CLOSED IN 2.5 MINUTES?

NO

NO

NO

NO

NO

YES

NO

GAS VALVE OFF. COMB. BLOWER ON. INDOORBLOWER (WITH 45 DELAY) ON. HAS CONTROL FAILEDFLAME SENSE 5 TIMES DURING ONE HEAT DEMAND?IF YES, SYSTEM GOES INTO 60 MIN.WATCHGUARD.DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF

NO, GO TO �COMB. AIR BLOWER ON?"IS FLAME SENSED AFTER 10 SECOND

FLAME RECTIFICATION PERIOD?

NO

NO

HAS CONTROL RESET IGNITION SEQUENCE 5 TIMESIF YES, SYSTEM GOES INTO 60 MIN. WATCHGUARD.DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF

NO, GO TO �COMB. AIR BLOWER ON?"

YES

YES

YES

YES

IGNITION TRIAL (10 seconds) −− START IGNITIONSPARK, OPEN MAIN GAS VALVE.

YES

80MGF WITH EGC−1 COOLING SEQUENCE OF OPERATION

YES



NO


1 SECOND DELAY. ACC TERMINAL ENERGIZED.

THERMOSTAT OPENS.

COMPRESSOR OFF.

SYSTEM FAN AND ACC TERMINAL OFF AFTER 0 SECONDS.

80MGF WITH EGC−1 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION

CONTINUOUS FAN SELECTION MADE AT THERMOSTAT.CONTROL ENERGIZES SYSTEM FAN AT LOW SPEED.

ACC TERMINAL ENERGIZED.



THERMOSTAT CALLS FOR COOLING.SYSTEM FAN SWITCHES TO HEAT SPEED AFTER

SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.

SYSTEM FAN SWITCHED TO COOLING SPEED. ACC TERMINAL REMAINS ENERGIZED.

SYSTEM FAN SWITCHES TO CONTINUOUS SPEEDAND ENERGIZES ACC TERMINAL. BOTH REMAIN ON

UNTIL CONTINUOUS FAN IS SWITCHED OFF AT THERMOSTAT.

YES NO

THERMOSTAT OPENS.

THERMOSTAT OPENS.

SYSTEM FAN SWITCHED OFF AFTER DELAY.ACC TERMINAL DE−ENERGIZED.

HTG ACC. TERM. ENERGIZEDWITH COMB. AIR BLOWER.

80MGF WITH SURELIGHT IGNITION CONTROL1 − When there is a call for heat, W1 of the thermostat en-

ergizes W of the furnace control with 24VAC.

2 − S10 primary limit switch and S47 rollout switch are

closed. Call for heat can continue.

3 − SureLight control energizes combustion air blower

B6. Combustion air blower runs until S18 combustion

air prove switch closes (switch must close within 2−1/2

minutes or control goes into 5 minute Watchguard

Pressure Switch delay). Once S18 closes, a 15−sec-

ond pre−purge follows.

4 − SureLight control energizes ignitor. A 20−second

warm−up period begins.

5 − Gas valve opens for a 4−second trial for ignition.

6 − Flame is sensed, gas valve remains open for the heat

call.

7 − After 45−second delay, SureLight control energizes

indoor blower B3.

8 − When heat demand is satisfied, W1 of the indoor ther-

mostat de−energizes W of the SureLight control which

de−energizes the gas valve. Combustion air blower

B6 continues a 5−second post−purge period, and in-

door blower B3 completes a selected OFF time delay.

SURELIGHT CONTROLHEATING SEQUENCE OF OPERATION



BURNER OFF?(CONTINUOUS FLAME CHECK)

NORMAL OPERATION:LED #1 −− SLOW FLASHLED #2 −− SLOW FLASH

YES

YES

YES

GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.INDOOR BLOWER DELAY OFF.

LED #1 ONLED #2 ON

(RESET CONTROL BY TURNING MAIN POWER OFF.)

POLARITY REVERSED.LED #1 −− FAST FLASHLED #2 −− SLOW FLASH

POWER ON

COMBUSTION AIR BLOWER ON FOR 1 SECOND.

TURN INDUCER ON FOR 1 SECOND.IS POLARITY REVERSED?

ROLLOUT SWITCH CLOSED?

THERMOSTAT CALLS FOR HEAT:LED #1 −− FAST FLASHLED #2 −− FAST FLASH

IS COMBUSTION AIRPRESSURE SWITCH OPEN?

GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.INDOOR BLOWER OFF WITH DELAY.LED #1 −− ON. LED #2 −− SLOW FLASH.

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.

GAS VALVE OFF. COMBUSTION AIR BLOWER ON.INDOOR BLOWER ON HEATING SPEED.

LED #1 −− SLOW FLASHLED #2 −− OFF

GAS VALVE OFF.COMBUSTION AIR BLOWER OFF.

INDOOR BLOWER OFF WITH DELAY.LED #1 OFF

LED #2 SLOW FLASH(Sequence holds until pressure switchcloses or thermostat resets control.)

NOYES

NO

IS THEREPROPER GROUND?

IS VOLTAGEABOVE 75 VOLTS?

LOW VOLTAGE SIGNAL AT LED HOLDSUNTIL VOLTAGE RISES ABOVE 75 VOLTS.

NOYES

NO

SIGNAL IMPROPERGROUND AT LED.SIGNAL HOLDSUNTIL UNIT IS

PROPERLYGROUNDED.

NO

NO

IS COMBUSTION AIR BLOWER ENERGIZED? (HTG ACC TERMINAL IS ENERGIZED WITH C.A.B.)

HAS COMBUSTION AIR PRESSURESWITCH CLOSED IN 2.5 MINUTES?

YES

YESPRESSURE SWITCH IS IN WATCHGUARD MODE.

GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.INDOOR BLOWER OFF WITH DELAY.

LED #1 −− OFF. LED #2 −− SLOW FLASH.IS 5-MINUTE RESET PERIOD COMPLETE?

NO

15-SECOND COMBUSTION AIR BLOWER PREPURGEINITIATED BY CLOSED PRESSURE SWITCH.

YES

YES

CONTINUED NEXT PAGE

YES

NO

GAS VALVE OFF. COMBUSTION AIR BLOWER ON.INDOOR BLOWER ON.

LED #1 ALTERNATING FAST FLASHLED#2 ALTERNATING FAST FLASHCHECK FOR BROKEN IGNITOR OR

OPEN IGNITOR CIRCUIT


FLAME RECTIFICATION CURRENTCHECK. CAN FLAME BE PROVEN WITHIN4 SECONDS AFTER GAS VALVE OPENS?

(�0.15 microamps)

FLAME PRESENT?

INDOOR BLOWER ON DELAY BEGINS(45 seconds.)

PRIMARY AND SECONDARY LIMITSWITCHES CLOSED?

COMBUSTION AIR PRESSURESWITCH CLOSED?

LOW FLAME SIGNAL(Does not affect operation of control)

LED #1 −− SLOW FLASHLED #2 −− FAST FLASH

GAS VALVE DE−ENERGIZED.COMBUSTION AIR INDUCER

DE−ENERGIZED.INDOOR BLOWERON UNTIL SWITCH CLOSES.LED #1

−− SLOW FLASH. LED #2 −− ON.IS LIMIT SWITCH CLOSED?

GAS VALVE DE−ENERGIZED.COMBUSTION AIR INDUCER ON.

INDOOR BLOWER OFF WITH DELAYLED #1 −− OFF. LED #2 −− SLOW FLASH.

HAS CAB SWITCH CLOSED IN 2.5 MINUTES?

15-SECOND COMBUSTION AIR INDUCER PREPURGEINITIATED BY CLOSED PRESSURE SWITCH.

YES

IGNITOR WARM-UP −− 20 SECONDS.

YES

4-SECOND TRIAL FOR IGNITION.GAS VALVE OPENS. IGNITOR ENERGIZED FOR

1 SECOND AFTER VALVE OPENS.NO FLAME SENSED DURING THIS PERIOD.

BOARD 97L48 ONLY: IGNITOR ENERGIZED FOR THEFULL 4−SECOND TRIAL FOR IGNITION.

YES

FLAME STABILIZATION PERIOD.

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.INDOOR BLOWER OFF.

HAS CONTROL FAILED TO SENSE FLAME FORFIVE CONSECUTIVE TRIES DURING A SINGLE

HEAT DEMAND?

IGNITION WATCHGUARD MODE. GAS VALVE OFF.COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH DELAYLED 1 ALT. SLOW FLASH LED 2 ALT SLOW FLASH

IS 60-MINUTE RESET PERIOD COMPLETE?

YES

4 SECONDS

YES

HAS CONTROL RESET IGNITIONSEQUENCE FOUR TIMES?

FLAME SIGNAL ABOVE 0.7 MICROAMPS?

YES

YES

HAS PRIMARY/SECONDARY LIMIT RESET.(See table 9 DIAGNOSTIC CODES for limit reset operation)

YES

ROLLOUT SWITCH CLOSED?

GAS VALVE POWER OFF. COMBUSTION AIR INDUCER POWER OFF.

INDOOR BLOWER OFF WITH DELAYLED #1 −− ON. LED #2 −− SLOW FLASH.

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET

YES

THERMOSTAT DEMAND SATISFIED.

LED #1 & #2 SIMULTANEOUS SLOW FLASHES.

YES

NO

5-MINUTE PRESSURE SWITCHWATCHGUARD MODE.

YES

IS THERE A PROPER GROUND?

IS VOLTAGE ABOVE 75 VOLTS?

IS IGNITOR INTACT AND CONNECTED?

LEDS SIGNAL ALTERNATINGFAST FLASH

NO YES

YESYES

YES

YES

NO

NO

NO

NO

NO

NO

NO

NO

YES

YES

NO

NO

NO

NO

YES

YES

LIMIT SWITCH WATCH GUARDMODE. GAS VALVE OFF.COMB. AIR INDUCER OFF. IN-DOOR BLOWER OFF WITHDELAY. LED#1−SLOW FLASHLED#2− ON. IS 60MINUTE RE-SET PERIOD COMPLETE.?

YES

YES

COMB. AIR INDUCER CONTINUES 5-SECOND POST PURGEAFTER T’STAT DEMAND IS SATISFIED. INDOOR AIR BLOWER

COMPLETES SELECTED �OFF" DELAY BEFORE SHUTTING OFF.ACB.HEAT SPEED, HTG ACC TERM. AND ACC TERM. OFF.

SURELIGHT CONTROLCOOLING SEQUENCE OF OPERATION

NORMAL COOLING MODE ABNORMAL COOLING MODE

IGNITION CONTROL MAIN POWER ON.

CONTROL SELF DIAGNOSTIC CHECK.IS CONTROL OPERATING NORMALLY?

YES

SIGNAL POLARITY REVERSED AT LED.

POWER ON

GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.INDOOR BLOWER OFF WITH NORMAL DELAY.

SIGNAL CIRCUIT BOARD FAILURE AT LED.INTERRUPT MAIN POWER TO RESET CONTROL.

YES

TURN INDUCER ON FOR 1 SECOND.

IS POLARITY REVERSED?

ROLLOUT SWITCH MONITORED CONTINUOUSLY.IS ROLLOUT SWITCH CLOSED?

CHECK FOR MAIN BURNER FLAME SENSE.IS MAIN BURNER FLAME OFF?

LED: SLOW FLASH RATE REMAINS UNCHANGEDTHROUGHOUT COOLING CYCLE.


COMPRESSOR CONTACTOR AND SYSTEM FANENERGIZED WITH 0-SECOND DELAY. ACB COOL

SPEED AND ACC. TERMINAL IS ENERGIZED.

COMPRESSOR OFF.

THERMOSTAT OPENS.

SYSTEM FAN AND ACC. TERM. OFFWITH 0-SECOND DELAY.

NO

YES

NO


SIGNAL CIRCUIT BOARD FAILURE AT LED.SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.

NO


SIGNAL CIRCUIT BOARD FAILURE AT LED.SEQUENCE HOLDS UNTIL FLAME IS NOT SENSED.

NO

IS THEREPROPER GROUND?

IS VOLTAGEABOVE 75 VOLTS?

LOW VOLTAGE SIGNAL AT LET HOLDSUNTIL VOLTAGE RISES ABOVE 75 VOLTS.

NOYES

NO

SIGNAL IMPROPERGROUND AT LED.SIGNAL HOLDSUNTIL UNIT IS

PROPERLYGROUNDED.

SURELIGHT CONTROLCONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION

LED: SLOW FLASH RATE REMAINSUNCHANGED THROUGHOUT SEQUENCE.

MANUAL FAN SELECTION MADE AT THERMOSTAT.CONTROL (G) ENERGIZES SYSTEM FAN AT ACBLOW SPEED. ACC. TERMINAL IS ENERGIZED.

THERMOSTAT CALLS FOR HEAT (W).


BOARD NO. 63K8901SYSTEM FAN DE−ENERGIZED. SYSTEM FANENERGIZES ON ACB HEAT SPEED AFTER

NORMAL DELAY.

THERMOSTAT OPENS. COMBUSTION AIRAND HTG ACC TERMINAL DE−ENERGIZE.

SYSTEM FAN SWITCHED TO ACB COOLSPEED. ACC. TERM. REMAINS ON.

THERMOSTAT OPENS.

BOARD 63K89: SYSTEM FAN OFF. ACC. TERM.OFF. (AFTER OFF DELAY COMPLETED).

MANUAL FAN SELECTION MADE AT THERMOSTAT.CONTROL (G) ENERGIZES SYSTEM FAN AT ACB

LOW SPEED. ACC. TERM. ENERGIZED.

NO YES

YESNO

HTG ACC. TERM. ENERGIZES WITH COMB. AIR BLOWER.

BOARD NO. 24L85, 56L83, 97L48SYSTEM FAN SWITCHES TO ACB HEAT SPEEDAFTER NORMAL DELAY (fan remains energized)

BOARDS 24L85, 56L83 AND 97L48:SYSTEM FAN SWITCHES TO

LOW SPEED AFTER NORMAL DELAY.(fan remains energized)

VIII−Troubleshooting−SureLight Control

PROBLEM: 1 UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE

Condition Possible Cause Corrective Action / Comments

1.1

− Both diagnostic lights fail to light up.

1.1.1

Main voltage 120V not supplied tounit.

ACTION 1 − Check 120V main voltage.Determine cause of main power failure.

LED#1−OffLED#2−Off

1.1.2

Miswiring of furnace or improperconnections.

ACTION 1 − Check for correct wiring of 120V topower make up box and transformer.ACTION 2 − Check 24V wiring to control board.

1.1.3

Circuit breaker tripped or fails toclose.

ACTION 1 − Replace circuit breaker if it is resetbut does not have continuity.ACTION 2 − If circuit breaker still trips, check forshort.

1.1.4

Door interlock switch failure.

ACTION 1 − Check that door switch is activatedwhen door is closed.ACTION 2 − Check wire connections to switch, re-place loose connectors.ACTION 3 − Check continuity of switch in closedposition. Replace if malfunctioning

1.1.5

Transformer Failure.

ACTION 1 − Check that transformer output is24V. Replace if malfunctioning

1.1.6

Failed control board.

ACTION 1 − If all the above items have beenchecked, replace board.

1.2

− Diagnostic lights flash the roll−out

code.

1.2.1

Roll−out switch open.

ACTION 1 − Manually reset the roll−out switchby pushing the top button.ACTION 2 − Determine the cause of the roll−outswitch activation before leaving furnace.code.

LED#1 O

1.2.2

Roll−out switch failure.

ACTION 1 − Check continuity across roll−outswitch. Replace roll−out switch if switch is resetbut does not have continuity.

LED#1−On,

LED#2−Slow Flash1.2.3

Mis iring or improper connections at ACTION 1 − Check wiring connections to switchLED#2 Slow FlashMiswiring or improper connections atroll−out switch.

ACTION 1 − Check wiring connections to switch.

1.2.4

Nine pin connector failure

ACTION 1 − Check 9−pin connector for properconnection to control board.ACTION 2 − Check continuity of the multi plugpin.

1.3

− On initial power−up the comb. airblower does not energize.blower does not energize. − Diagnostic lights flash the reversepolarity code.

1.3.1

120V main power polarity reversed.

ACTION 1 − Check the 120V has line and neutralcorrectly input into control.ACTION 2 − Reverse the line and neutral at the120V field connection.

LED#1−Fast Flash,LED#2−Slow Flash.

120V field connection.

1.4

− On initial power up the combustionair blower does not energize. − Diagnostic lights flash normal poweron operation.

1.4.1

Open combustion air blower motorcircuit.

ACTION 1 − Check for 120V to combustion airblower. If no power, check wire and connec-tions.

on operation.

LED#1−Slow FlashLED#2−Slow Flash

1.4.2

Failed combustion air blower motor.

ACTION 1 − If power is present at blower, replaceblower.

PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE


1.5

− On initial power−up the combustionair blower remains energized.

Di ti li ht fl h th i

1.5.1

Improper ground to the unit.

ACTION 1 − Check that the unit is properlygrounded.ACTION 2 − Install a proper main ground to theunitg

− Diagnostic lights flash the impropermain ground.

1.5.2

6−Pin connector is improperly at-tached to the circuit board.

ACTION 1 − Check 6−pin connector for properinstallation. Correctly insert connector into con-trol.

LED#1−Alternating Fast FlashLED#2−Alternating Fast Flash

1.5.3

Line voltage is below 75V.

ACTION 1 − Check that the line voltage is above75V. Determine cause of voltage drop and sup-ply correct voltage to the control.

PROBLEM 2: UNIT FAILS TO OPERATE IN THE COOLING OR HEATING MODE, BUT COMBUS-TION AIR BLOWER OPERATES CONTINUOUS. UNITS WITH CONTROL BOARDS DATE CODEDAFTER NOV.1 1997, WILL OPERATE IN COOLING WITH COMBUSTION AIR BLOWER CYCLING

5 SECONDS ON 55 SECONDS OFF, BUT NOT IN THE HEATING MODE.


2.1

− On initial power−up the combustionair blower remains energized. − Diagnostic lights flash the impropermain ground. − Units with control boards datecoded after Nov 1 1997; combustion

2.1.1

Open ignitor circuit.

ACTION 1 − Check for correct wiring and looseconnections in the ignitor circuit. Check multi −plug connections for correct installation.

coded after Nov.1 1997; combustionair blower will cycle 5 seconds on 55seconds off.

LED#1−Alternating Fast FlashLED#2−Alternating Fast Flash

2.1.2

Broken or failed ignitor.

ACTION 1 − Unplug ignitor and read resistanceacross ignitor. If resistance does not read be-tween 10.9 and 19.7 ohms, replace the ignitor.

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOESNOT ENERGIZE


3.1

− Unit operates with a cooling or con-tinuous fan demand. − Combustion air blower will not startwith a Heating demand. − Diagnostic lights flash the limit failure

d

3.1.1

Primary or secondary (if equipped)limit open.

ACTION 1 − Check continuity across switch(es).Switches reset automatically upon cool down.ACTION 2 − Check for restrictions on blower inletair (including filter) and outlet air. Determinecause for limit activation before placing unit backin operation.

g gmode.

LED#1−Slow Flash,LED#2−On

3.1.2

Miswiring of furnace or improper con-nections at limit switch(es).

ACTION 1 − Check for correct wiring and looseconnections. Correct wiring and/or replace anyloose connections.

3.2

− Unit operates with a cooling and con-tinuous fan demand. − Combustion air blower will not startwith a Heating demand. − Diagnostic lights flash the pressure

3.2.1

Miswiring of furnace or improper con-nections to combustion air blower.


− Diagnostic lights flash the pressureswitch failure code.

LED#1−Off,LED#2−Slow Flash

3.2.2

Pressure switch stuck closed.

ACTION 1 − Check that the pressure switch isopen without the combustion air blower operat-ing. Replace if malfunctioning

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOESNOT ENERGIZE (CONT.).

Condition Possible Cause Corrective Action/Comments

3.3

− Unit operates with a cooling and con-tinuous fan demand. − Combustion air blower will not startwith a Heating demand. − Diagnostic lights flash the pressureswitch failure code 2 5 minutes after

3.3.1

Miswiring of furnace or improper con-nections to combustion air blower.


switch failure code 2.5 minutes afterheating demand.

LED#1−Off, LED#2−Slow Flash

3.3.2

Combustion air blower failure.

ACTION 1 − If there is 120V to combustion airblower and it does not operate, replace combus-tion air blower.

PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER ENERGIZES, IGNITOR IS NOT ENERGIZED.


4.1

− Unit operates with a cooling andcontinuous fan demand. − Combustion air blower energizeswith a heating demand

4.1.1

Pressure switch does not close dueto incorrect routing of the pressure

switch tubing.

ACTION 1 − Check that the pressure switch tub-ing is correctly routed. Correctly route pressureswitch tubing.

with a heating demand. − Diagnostic lights flash the pressureswitch failure code 2.5 minutes afterheating demand.

4.1.2

Pressure switch does not close dueto obstructions in the pressure tub-

ing.

ACTION 1 − Remove any obstructions from thepressure tubing and/or taps.

LED#1−OffLED#2−Slow Flash

4.1.3

Pressure switch tubing damaged

ACTION 1 − Check pressure switch tubing forleaks. Replace any broken tubing.

LED#2 Slow Flash

4.1.4

Pressure switch does not close dueto a low differential pressure across

the pressure switch.

ACTION 1 − Check the differential pressure

across the pressure switch. This pressure

should exceed the set point listed on the

switch.

ACTION 2 − Check for restricted inlet and ex-

haust vent. Remove all blockage.

ACTION 3 − Check for proper vent sizing and

run length. See installation instructions.

ACTION 4 − Check voltage to combustion air

blower.

4.1.5

Wrong pressure switch installed inthe unit, or pressure switch is out of

calibration.

ACTION 1 − Check that the proper pressureswitch is installed in the unit. Replace pressureswitch if necessary.

4.1.6

Miswiring of furnace or improper con-nections at pressure switch.


4.1.7

Pressure switch failure.

ACTION 1 − If all the above modes of failure havebeen checked, the pressure switch may havefailed. Replace pressure switch and determine ifunit will operate.

PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)


5.1

− Unit operates with a cooling and

continuous fan demand.

Combustion air blower energizes

5.1.1

Check that gas is being supplied tothe unit.

ACTION 1 − Check line pressure at the gasvalve. Pressure should not exceed 13" WC forboth natural and propane. Line pressure shouldread a minimum 4.5" WC for natural and 8.0"WCfor propane.

− Combustion air blower energizes

with Heating demand.

− Ignitor is energized but unit fails to

light.

5.1.2

Miswiring of gas valve or loose con-nections at multi−pin control amp

plugs or valve.


LED#1−Alternating Slow Flash

LED#2−Alternating Slow Flash

5.1.3

Malfunctioning gas valve or ignitioncontrol.

ACTION 1 − Check that 24V is supplied to thegas valve approximately 35 seconds after heatdemand is initiated.ACTION 2 − Replace the valve if 24V is suppliedbut valve does not open (check for excessivegas line pressure before replacing gas valve).ACTION 3 − Replace the control board if 24V isnot supplied to valve.

PROBLEM 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY


6.1

− Burners fire with a heating de-mand. − Burners light but unit shuts off priorto satisfying T−stat demand. − Diagnostic lights flash the pressureswitch code.

LED#1−OffLED#2−Slow Flash

6.1.1

Low pressure differential at the pres-sure switch.

ACTION 1 − Check for restricted vent inlet or ex-haust. Remove all blockage.ACTION 2: Check for proper vent sizing. Seeinstallation instructions.

6.2

− Combustion air blower energizeswith a heating demand.

B li ht b t f il t t lit

6.2.1

Sensor or sense wire is improperlyinstalled.

ACTION 1 − Check that sensor is properly lo-cated (page 10) and that the sense wire isproperly attached to both the sensor and thecontrol.

− Burners light but fail to stay lit. − After 5 tries the control diagnosticsflash the watchguard burners failed toignite code.

6.2.2

Sensor or sense wire is broken.

ACTION 1 − Check for a broken sensor.ACTION 2 − Test continuity across the sensewire. If wire or sensor are damaged replacethe component.ignite code.

LED#1−Alternating Slow FlashLED#2−Alternating Slow Flash

6.2.3

Sensor or sensor wire is grounded tothe unit.

ACTION 1 − Check for resistance between thesensor rod and the unit ground.ACTION 2 − Check for resistance between thesensor wire and the unit ground.ACTION 3 − Correct any shorts found in circuit.

6.2.4

Control does not sense flame.

ACTION 1 − Check the microamp signal fromthe burner flame. If the microamp signal is be-low 0.70 microamps, check the sense rod forproper location or contamination.ACTION 2 − Replace, clean, or relocate flamesense rod. If rod is to be cleaned, use steelwool or replace sensor. DO NOT CLEAN RODWITH SAND PAPER. SAND PAPER WILLCONTRIBUTE TO THE CONTAMINATIONPROBLEM. NOTE: Do not attempt to bendsense rod.

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY (CONT.)


6.3

− Combustion air blower energizeswith a heating demand. − Burners light. − Roll−out switch trips during theheating demand. − Diagnostic lights flash roll−out fail-ure.

6.3.1

Unit is firing above 100% of thenameplate input.

ACTION 1 − Check that the manifold pressurematches value listed on nameplate. See installa-tion instructions for proper procedure.ACTION 2 − Verify that the installed orifice sizematch the size listed on the nameplate or instal-lation instructions.ACTION 3 − Check gas valve sensing hose to in-sure no leaks are present.ACTION 4 − Check the input rate to verify ratematches value listed on nameplate.ure.

LED#1−OnLED#2−Slow Flash

6.3.2

Gas orifices leak at the manifold con-nection.

ACTION 1 − Tighten orifice until leak is sealed.NOTE: Be careful not to strip orifice threads. AC-TION 2 − Check for gas leakage at the threadedorifice connection. Use approved method forleak detection (see unit instructions).

6.3.3

Insufficient flow through the heat ex-changer caused by a sooted or re-

stricted heat exchanger.

ACTION 1 − Check for sooting deposits or otherrestrictions in the heat exchanger assembly.Clean assembly as outlined in instruction manu-al.ACTION 2 − For 80MGF gas furnaces, check forproper combustion and flow. CO2 should mea-sure between 6.0% and 8.0% for natural and6.5% and 8.5% for L.P. CO should measure be-low .04% (400PPM) in an air−free sample of fluegases.

6.3.4

Burners are not properly located inthe burner box.

ACTION 1 − Check that the burners are firing intothe center of the heat exchanger openings. Cor-rect the location of the burners if necessary.

6.4

− Combustion air blower energizeswith a heating demand. − Burners light roughly and the unitfails to stay lit. − Diagnostic lights flash watchguardflame failure.

6.4.1

Recirculation of flue gases. This con-dition causes rough ignitions and op-eration. Problem is characterized by

nuisance flame failures.

ACTION 1 − Check for proper flow of exhaustgases away from intake vent. Remove any ob-stacles in front of the intake and exhaust ventwhich would cause recirculation.ACTION 2 − Check for correct intake and ex-haust vent installation. See instructions

flame failure.


6.4.2

Improper burner cross−overs

ACTION 1 − Remove burner and inspect thecross−overs for burrs, or any restriction or ifcrossover is warped. Remove restriction or re-place burners.

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY (CONT.)

6.5

− Combustion air blower energizeswith a heating demand. − Burners light. − Diagnostic lights flash watch guardflame failure. − NOTE" Unit might go into 60 min-ute Watchguard mode depending onintermittent nature of sensor signal.


6.5.1

Loose sensor wire connectioncauses intermittent loss of flame sig-

nal.

ACTION 1 − Check that the sensor is properly lo-cated.ACTION 2 − Check that the sense wire is proper-ly attached to both the sensor and the control.Pay extra attention to the pin connectors.

PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE


7.0

− Unit operates correctly but thediagnostic lights flash low flamesense code

7.1.1

Sense rod is improperly located onthe burner.

ACTION 1 − Check the sense rod for proper loca-tion on the burner. Properly locate the sense rodor replace if rod cannot be located correctly.

sense code.

LED#1−Slow FlashLED#2−Fast Flash

7.1.2

Sense rod is contaminated.

ACTION 1 − Check sense rod for contaminationor coated surface. Clean the sense rod with steelwool or replace sensor. DO NOT USE SAND PA-PER TO CLEAN ROD. SAND PAPER WILLCONTRIBUTE TO THE CONTAMINATIONPROBLEM.

PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUSFAN MODE


8.0

− Indoor blower fails to operate incontinuous fan, cooling, or heatingmode.

8.1.1

Miswiring of furnace or improper con-nections at control or indoor blower

motor.

ACTION 1− Correct wiring and/or replace anyloose connections. Check for correct wiring andloose connections.

8.1.2

120V is not being supplied to the in-door air blower or blower motor fail-

ure.

ACTION 1 − Check for 120V at the various callsfor indoor blower by energizing "Y", "G", and "W"individually on the low voltage terminal strip.Note that when "W’ is energized, the blower isdelayed 45 seconds. If there is 120V to each mo-tor tap but the blower does not operate, replacethe motor.

8.1.3

Defective control board

ACTION 1 − If there is not 120V when "Y", "G", or"W" is energized, replace the control.

PROBLEM 9: RF STATIC DURING TIME FOR IGNITION


9.0− AM radio interference

9.1.2Ignitor operation

ACTION 1− Call Technical Support, Dallas

SERVICE NOTES

80mgf - furnaces

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