Lennox AC Error Codes (Troubleshooting Guide)

If any error occurs in your air conditioner, indoor display shows error codes. Once you nail down the issue you can easily call in a professional, or fix the issue yourself. To help you out we have listed down the most common error codes of Lennox AC.

Indoor Unit Display Codes

Error CodesCause
E0EEPROM parameter error
E1Indoor/outdoor units communication protection
E2Zero-crossing signal error
E3Indoor fan speed out of control
E5Open or short circuit of outdoor temperature sensor or outdoor unit EEPROM parameter error
E6Open or short circuit of room or evaporator temperature sensor
E7Outdoor fan speed out of control
P0IBM malfunction or IGBT over-strong current protection
P1Over voltage or too low voltage protection
P2Temperature protection of compressor top
P4Inverter compressor drive error

Split Type AC Codes

Lennox Split AC Error Codes
Lennox Split AC Error Codes

If there is an error occurring during the operation of the system, the error code will be displayed on the LCD, as show in Fig.5.1. If multi errors occur at the same time, their codes will be displayed circularly.

Error CodesMeaning
E1High pressure protection.
E2Anti-freezing protection.
E3Low pressure protection.
E4High discharge temperature protection.
E5Whole unit over-current protection.
E6Indoor and outdoor communication error.
E7Running mode conflict.
E8Overload protection.
E9Indoor unit full water error.
ENCurrent protection.
EUFrequency restricted/reduced with IPM temperature protection.
EL0CRefrigerant leakage detection.
EH61Evaporator coil middle temperature sensor T2 is in open circuit or has short circuited.
F0System charge shortage or blockage protection.
F1Return air temperature sensor open/ short circuited.
F2Evaporator temperature sensor open/ short circuited.
F3Outdoor ambient temperature sensor open/ short circuited.
F4Outdoor unit condenser mid-tube temperature sensor open/short circuited.
F5Discharge temperature sensor open/ short circuited.
F6Frequency restricted/reduced with overload protection.
F8Frequency restricted/reduced with whole unit current protection.
F9Frequency restricted/reduced with high discharge temperature.
FHFrequency restricted/reduced with antifreezing protection.
H1Forced defrosting.
H3Compressor overheating protection.
H5IPM Current protection.
H6Motor stalling.
H7 Compressor desynchronizing.
HCPFC protection.
HECompressor demagnetization protection.
P5Over phase current protection.
P6Drive board communication error.
P7IPM temperature sensor open/short circuited.
P8IPM Temperature Protection.
P9AC contactor protection.
PDSensor connection protection.
PETemperature drift protection.
PFDrive board temperature sensor error.
PHDC bus over-voltage protection.
PLDC bus under-voltage protection.
PPAC input voltage abnormal.
PUCapacitor charging error.
PC00Inverter module IPM error.
PC01High or Low voltage protection.
PC02High temperature sensed at compressor top.
PC03Low or High pressure protection.
PC04Inverter compressor drive error.
PC08Current overload protection.
PC0LOutdoor low ambient temperature protection.
U1Compressor phase current sensing circuit error.
U3DC bus voltage drop error.
U5Whole unit current sensing circuit error.
U74-way valve reversing error.
U8PG motor zero-crossing protection.
L3Outdoor fan 1 error protection.
L9Over-power protection.
LAOutdoor fan 2 error protection.
LCCompressor startup failure.
LDCompressor phase loss/reversal protection.
LECompressor stalling.
LPIndoor and outdoor units unmatched.
B5Indoor unit liquid valve temperature sensor open/short circuited.
B7Indoor gas valve temperature sensor open/ short circuited.
C5Jumper error.
DNCommunication line misconnected or expansion valve error.
105Device communication failure
120Unresponsive device
124Active subnet controller missing
125Hardware failure
126Internal control communication failure
131Corrupted control parameters
132Failed flash CRC check
180Ambient sensor problem
400Compressor internal overload trip
401Long run time. Compressor is running extremely long run cycles
402System pressure trip.
403Short cycling. Compressor is running less than three minutes
404Locked rotor. Compressor has a locked out due to run capacitor short, bearings are seized, excessive liquid refrigerant
405Open circuit.
406Open start circuit
407Open run circuit
408Welded contactor. Compressor always runs
409Secondary low voltage.
410Low pressure fault
411Low pressure switch lockout
412High pressure fault
413High pressure switch lockout
414Discharge line temperature fault
415Discharge line temperature lockout
417Discharge sensor fault
Ds11, Ds13, Ds14, Ds15OEM mode. Factory test mode

Note: In event of any error, please turn off the unit and contact the professionally skilled personnel.

Remote Control Buttons Meaning

Lennox AC Remote Control
Lennox AC Remote Control

Mini Split Type Codes

Lennox Air Conditioner Mini Split Error Codes
Lennox Air Conditioner Mini Split Error Codes

Indoor and Outdoor Error Codes


Rooftop Codes

Climatic 50 Roof-Top, Aircoolair & Compactair Version 24

Error CodesProblem
004Filters, Clogged up
005Filters, Missing
006Recovery Module, Filters, Clogged up
011Electric heating elements
012High Temperature, Blowing
013Low Temperature, Ambient
022Low Temperature, Blowing
023High Temperature, Ambient
051Recovery Module, Motor failure
052Recovery Module, Wheel failure
081Temperature sensor, Ambient
082Humidity sensor, Ambient
083Temperature probe, Outside
084Humidity sensor, Outside
085Temperature probe, Blower
086Circuit 1, Temperature sensor, Water condenser Outlet
087Circuit 2, Temperature sensor, Water condenser Outlet
088Temperature sensor, return or Mixing air
096Low temperature, Water Condenser
097High temperature, Water Condenser


Please check below items before asking for maintenance.

Phenomenon: Indoor unit can’t receive remote controller’s signal or remote controller has no action.

Check items:

  1. Whether remote controller is within the signal receiving range?
  2. Whether there are obstacles?
  3. Whether remote controller is pointing at the receiving window?
  4. Is sensitivity of remote controller low; fuzzy display and no display?
  5. No display when operating remote controller?
  6. Fluorescent lamp in room?


  1. Signal receiving range is 8m.
  2. Remove obstacles.
  3. Select proper angle and point the remote controller at the receiving window on indoor unit.
  4. Check the batteries. If the power of batteries is too low, please replace them.
  5. Check whether remote controller appears to be damaged. If yes, replace it.
  6. Take the remote controller close to indoor unit.

Phenomenon: No air emitted from indoor unit

Check items:

  1. Air inlet or air outlet of indoor unit is blocked?
  2. Under heating mode, indoor temperature is reached to set temperature?
  3. Heating mode is turned on just now?


  1. Eliminate obstacles.
  2. After reaching to set temperature, indoor unit will stop blowing out air.
  3. In order to prevent blowing out cold air, indoor unit will be started after delaying for several minutes, which is a normal phenomenon.

Phenomenon: Air conditioner can’t operate

Check items:

  1. Power failure?
  2. Is plug loose?
  3. Air switch trips off or fuse is burnt out?
  4. Wiring has malfunction?
  5. Unit has restarted immediately after stopping operation?
  6. Whether the function setting for remote controller is correct?


  1. Wait until power recovery.
  2. Reinsert the plug.
  3. Ask professional to replace air switch or fuse.
  4. Ask professional to replace it.
  5. Wait for 3min, and then turn on the unit again.
  6. Reset the function.

Phenomenon: Mist is emitted from indoor unit’s air outlet

Check items: Indoor temperature and humidity is high?

Solution: Because indoor air is cooled\rapidly. After a while, indoor temperature and humidity will be decrease and mist will disappear.

Phenomenon: Cooling ( heating) effect is not good

Check items:

  1. Voltage is too low?
  2. Filter is dirty?
  3. Set temperature is in proper range?
  4. Door and window are open?


  1. Wait until the voltage resumes normal.
  2. Clean the filter.
  3. Adjust temperature to proper range.
  4. Close door and window.

Phenomenon: Outdoor unit has vapor

Check items: Heating mode is turned on?

Solution: During defrosting under heating mode, it may generate vapor, which is a normal phenomenon.

Phenomenon: ”Water flowing” noise

Check items: Air conditioner is turned on or turned offjust now?

Solution: The noise is the sound of \refrigerant flowing inside the unit, which is a normal phenomenon.

Phenomenon: Cracking noise

Check items: Air conditioner is turned on or turned offjust now?

Solution: This is the sound of frictioh caused by expansion and/or contraction of panel or other parts clue to the change of temperature.

Manual Pdf

Lennox Air Conditioner Manual PDF

Lennox Rooftop Service Manual

*If you can't find the code you're looking for on our site, please let us know, and we'll update our database as soon as possible.

13 thoughts on “Lennox AC Error Codes (Troubleshooting Guide)”

    • Hello Nclave, first of all, thank you for visiting our website.

      If your air conditioner is still under warranty, the best option would be to call in a service team. The service team will diagnose the issue and take the necessary steps for repair.

      However, if the warranty has expired or you’re looking for a quicker solution, there are a few steps you can try yourself.

      E410 Low pressure fault.

      Possible Causes:

      1. Restricted air flow over indoor or outdoor coil.
      2. Improper refrigerant charge in system.
      3. Improper metering device installed or incorrect operation of metering device.
      4. Incorrect or improper sensor location or connection to system.

      If these steps do not work, I would recommend reaching out to the technical service of the device. I hope this issue gets resolved quickly and your air conditioner works smoothly again. If you have any questions or need further assistance, please let me know.


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