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Error code reference
Lennox Air Conditioner Error Codes
51 error codes documented with diagnostic procedures.
Have your model number? Get codes specific to your unit.
1Power loss for two electrical cycles (33-40 milliseconds), suggesting dirty or low…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 indicate…5Pressure switch opens after compressor has run for more than two minutes, may indicate…6Compressor temperature exceeded its limit after running less than five minutes (or open…7Compressor temperature exceeded its limit after running more than five minutes (or open…8Option 1 safety device switch opens after compressor runs less than five minutes.9Option 1 safety device switch opens after compressor runs more than five minutes.E105The outdoor control has lost communication with either the thermostat or indoor unit due…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 more than…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 control will…E345The 'O' relay on the outdoor board has failedE409Outdoor control secondary voltage is 18VAC or less; after 10 minutes, operation is…E410The outdoor unit low pressure switch has closed indicating unit pressure is below the…E411The low pressure switch has opened 5 times within one hour, locking out the outdoor unit.E412The outdoor unit high pressure switch has opened indicating unit pressure is above the…E413The high pressure switch has opened 5 times within one hour, locking out the outdoor unit.E416The outdoor coil sensor has malfunctioned (open, shorted, or out of range); outdoor unit…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 return due…E426Excessive inverter alarmsE427The inverter has detected a DC peak fault condition (55A or higher), causing compressor…E428The inverter has detected a high main input current condition (inverter code 22).E429DC link power in inverter does not rise above threshold (180 VDC for 2/3-ton, 250 VDC for…E430Compressor start failure detected by inverter (inverter code 26).E431PFC detected an over-current condition of 100A (inverter code 27), indicating power…E432The inverter has detected a DC link high voltage conditionE433The inverter has detected a compressor over-current condition (peak phase current greater…E434Outdoor control has lost communications with the inverter for greater than 3 minutes…E435Inverter internal error (inverter code 60); outdoor control cycles power to the inverter.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 condition…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 outdoor unit.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
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Common questions
How do I find the error code on my Lennox Air Conditioner?
Most Lennox air conditioners show the code directly on the control panel display. If your model has no display, it can be read by entering diagnostic mode with the key sequence for your model. The full procedures include model-specific instructions for reading codes.
Are these codes specific to my model?
The codes here apply broadly to Lennox air conditioners. Meanings and diagnostic steps can vary by model and production year, so enter your model number for model-specific information and procedures.
What do I do if my code is not listed?
Some codes are model-specific or only appear in diagnostic mode. Enter your model number to get codes specific to your unit, or contact us. We update the database continuously from manufacturer service documentation.
How much does it cost to access the full diagnostic procedures?
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