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Lennox Air Conditioner Error Codes
51 error codes for Lennox air conditioner models. Each links to the full diagnostic procedure from the service manual.
CodeDescription
1Power loss for two electrical cycles (33-40 milliseconds), suggesting dirty or…10Option 2 safety device switch opens.11Compressor temperature sensor wires have shorted together.14Control is in TEST mode; does not indicate a problem.15Mode jumper is not in place on the TSC5 two-speed control.2Input indication3Unsteady thermostat input4Pressure switch opens after compressor has run for less than two minutes, may…5Pressure switch opens after compressor has run for more than two minutes, may…6Compressor temperature exceeded its limit after running less than five minutes…7Compressor temperature exceeded its limit after running more than five minutes…8Option 1 safety device switch opens after compressor runs less than five…9Option 1 safety device switch opens after compressor runs more than five…E105The outdoor control has lost communication with either the thermostat or indoor…E120There is a delay in the outdoor unit responding to the system.E124The iComfort Wi-Fi thermostat has lost communication with the outdoor unit for…E125There is a hardware problem with the outdoor control.E131The outdoor unit control parameters are corrupted.E132Internal software error on the outdoor control.E180The outdoor unit ambient temperature sensor has malfunctioned; outdoor unit…MyPros+ Max
Get the full diagnostic procedure for any Lennox air conditioner error code.
- Step-by-step tests with expected resistance, voltage, and continuity values
- Wiring diagram references and connector pinouts
- Verified part numbers when replacement is required
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E345The 'O' relay on the outdoor board has failedE409Outdoor control secondary voltage is 18VAC or less; after 10 minutes, operation…E410The outdoor unit low pressure switch has closed indicating unit pressure is…E411The low pressure switch has opened 5 times within one hour, locking out the…E412The outdoor unit high pressure switch has opened indicating unit pressure is…E413The high pressure switch has opened 5 times within one hour, locking out the…E416The outdoor coil sensor has malfunctioned (open, shorted, or out of range)…E422Compressor top cap switch exceeding thermal limit.E423The inverter has detected a circuit problem (inverter code 40).E424The liquid line temperature sensor has malfunctioned (open or shorted).E425Outdoor control has increased minimum compressor speed to allow for proper oil…E426Excessive inverter alarmsE427The inverter has detected a DC peak fault condition (55A or higher), causing…E428The inverter has detected a high main input current condition (inverter code…E429DC link power in inverter does not rise above threshold (180 VDC for 2/3-ton…E430Compressor start failure detected by inverter (inverter code 26).E431PFC detected an over-current condition of 100A (inverter code 27), indicating…E432The inverter has detected a DC link high voltage conditionE433The inverter has detected a compressor over-current condition (peak phase…E434Outdoor control has lost communications with the inverter for greater than 3…E435Inverter internal error (inverter code 60); outdoor control cycles power to the…E436Inverter heat sink temperature exceeded limit (inverter code 62).E437Heat sink temperature sensor fault has occurredE438The inverter has detected a PFC over current condition caused by a high load…E439Compressor slowdown due to high input currentE440Heat sink temperature is approaching limit (inverter code 13); compressor speed…E441Compressor slowdown due to high compressor currentE442The top cap switch has opened five times within one hour, locking out the…E443Incorrect appliance unit size code selected.E600Compressor has been cycled OFF on utility load shedding.E601Outdoor unit has been cycled OFF on low temperature protection