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Air ConditioningAir Conditioning
Starting RelaysStarting Relays
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Starting RelaysStarting Relays
Purpose• Remove the start winding
and/or start capacitor from the circuit
• Compressor start relays are mounted outside the motor
• Centrifugal switch could not be used in hermetic motor
Purpose• Remove the start winding
and/or start capacitor from the circuit
• Compressor start relays are mounted outside the motor
• Centrifugal switch could not be used in hermetic motor
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Types of RelaysTypes of Relays
• These are the three most common• The HP of the motor will
determine what type will be used• Service man may replace not
re-design.
• These are the three most common• The HP of the motor will
determine what type will be used• Service man may replace not
re-design.
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Three types
• Current Coil Relay• Solid State Relay or PTC• Potential Relay
Three types
• Current Coil Relay• Solid State Relay or PTC• Potential Relay
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Current Coil RelayCurrent Coil Relay• Works off amperage to the run winding.• On compressor start up:–Motor draws high current – Induces a strong magnetic field in the
relay’s magnetic coil through the run winding–This magnetic field lifts a plunger with
contacts and a counter tension spring–Contacts to start winding are made–Start winding is energized
• Works off amperage to the run winding.• On compressor start up:–Motor draws high current – Induces a strong magnetic field in the
relay’s magnetic coil through the run winding–This magnetic field lifts a plunger with
contacts and a counter tension spring–Contacts to start winding are made–Start winding is energized
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• Motor now starts because start windingcreates a strong magnetic field
• Motor reaches 75% running capability:• Current drops down• Relay coil is in series with run winding• Not enough current remains to keep coil
magnetized• Spring pushes plunger down• START WINDING IS DE-ENERGIZED
• Motor now starts because start windingcreates a strong magnetic field
• Motor reaches 75% running capability:• Current drops down• Relay coil is in series with run winding• Not enough current remains to keep coil
magnetized• Spring pushes plunger down• START WINDING IS DE-ENERGIZED
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• Used mainly on fractional horsepower compressors for small refrigeration units, not A/C
• Used mainly on fractional horsepower compressors for small refrigeration units, not A/C
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Solid State Relay Solid State Relay• Also works off current• Has materials that changes its
resistance• PTC-Positive Temperature Coefficient• Temp goes up/ resistance goes up• Wired in series with start winding only
• Also works off current• Has materials that changes its
resistance• PTC-Positive Temperature Coefficient• Temp goes up/ resistance goes up• Wired in series with start winding only
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• Uses up voltage (loads in series)• Example:–Voltage drop across relay would be 110v–Voltage drop across start winding 10v
• REMEMBER series law (Et=E1+E2…)
• Uses up voltage (loads in series)• Example:–Voltage drop across relay would be 110v–Voltage drop across start winding 10v
• REMEMBER series law (Et=E1+E2…)
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• Solid State relays have a greater range
• Example: 1 SS relay may be used for–1/16 to 3/4 Hp motor–3/4 to 2 HP motor
• If a current coil was used different relays would be needed.
• Solid State relays have a greater range
• Example: 1 SS relay may be used for–1/16 to 3/4 Hp motor–3/4 to 2 HP motor
• If a current coil was used different relays would be needed.
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Types of Solid State relaysTypes of Solid State relays
• Two wire is relay only• Five wire is start capacitor, relay
and overload• Testing:–When Ohmming them out, a good relay will have a (low) resistance reading–Must cool down before testing
• Two wire is relay only• Five wire is start capacitor, relay
and overload• Testing:–When Ohmming them out, a good relay will have a (low) resistance reading–Must cool down before testing
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Potential RelayPotential Relay
• Operates from voltage created by start winding• Also known as –Back Electromotive Force, or Back EMF
• Operation• Contacts are N.C. and allow full
voltage to start winding
• Operates from voltage created by start winding• Also known as –Back Electromotive Force, or Back EMF
• Operation• Contacts are N.C. and allow full
voltage to start winding
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• Terminals that are used and how to wire potential relay (this is the ONLY way)–Line to start capacitor–Start capacitor to TERM #1–TERM #2 to start winding–TERM #5 to common terminal
• All other terminals are blanks
• Terminals that are used and how to wire potential relay (this is the ONLY way)–Line to start capacitor–Start capacitor to TERM #1–TERM #2 to start winding–TERM #5 to common terminal
• All other terminals are blanks
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Checking the Potential relay with OhmmeterChecking the Potential relay with Ohmmeter
–Term #1 to Term #2•Continuity
–Term #1 to Term #5•Ohm Reading•Ex. 2k ohms
• The same for Term #2 to Term #5
–Term #1 to Term #2•Continuity
–Term #1 to Term #5•Ohm Reading•Ex. 2k ohms
• The same for Term #2 to Term #5
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