Common Error Fault Codes in Air Conditioners

Whether you have a ducted air conditioner, split system, multi-zone or a commercial air conditioning unit, you may see a dreaded error code appear on your master controller. Some may be an easy fix, such as simply resetting your air conditioner and clearing the onboard memory while others require professional assistance.

In this article, we will go over general reasons for receiving an error code, general air conditioning faults, UF / UP / U6 fault code on Mitsubishi Electric ducted systems and common LG split system faults.

There are many possibilities as to why your master controller may be displaying error codes or why your system is not responding.

Potential reasons across a range of air conditioners include:

  • The system needs re-gassing
  • Old age (wear and tear)
  • Technical faults
  • Unforeseen weather events
  • Animals damaging the system in the roof or the outdoor unit
  • Air conditioner not switched on at the control
  • The circuit breaker has tripped
  • Vermin may have chewed through controller wiring
  • Blown council service fuse
  • Your local power supplier may be doing works to your areas power supply
  • Internal fault in the air conditioner
  • Defrosting
  • Compressor delay after a restart
  • Delayed fan start on heating


If moulded case circuit breakers or earth leakage circuit breakers have tripped, do not reset the breaker immediately without first checking, or have your technician check for any problems with insulation of equipment. Resetting breakers without a check of insulation may cause damage to equipment.

By ‘resetting’ your air conditioner, what we mean is deleting the air conditioners on board memory to try a fresh restart. While not always successful, it is the first step in trying to save money with a service call. Some faults are caused by lightning strikes, blackouts and brownouts or various power fluctuations caused by any number of things and just may be the cause of your air conditioner shutting down for safety reasons.

How to reset your air conditioning error codes. (Note: we are NOT resetting circuit breakers that have tripped.)

Isolator Switch Master Reset. Go to your outdoor unit.

  1. Locate the isolator switch on the unit or on the wall beside the unit, which looks like a commercial on/off switch.
  2. Turn the switch off and leave it off for an hour.
  3. Turn the isolator switch back on after an hour.
  4. Turn the unit back on from the master controller and see how the system runs.

Turning off the isolator switch will cut the power from the switchboard and clear the memory of the air conditioning functions it was doing beforehand.


General Air Conditioning Error Codes (Fault Codes)

There are many hundreds of error codes that are used within the air conditioning industry, and they are mostly different across different manufacturers and across their different models, and we won’t list them all. Below is a short list of common error codes from a couple of major air conditioner manufacturers.

This is a general summary of the error codes you may see on your air conditioner.

Error codes A0 to AJ, go from an indoor error of external protection device, to a PCB defect, to a malfunction of EEV, the indoor fan motor lock is overloaded and a malfunction of capacity set device.

C3 to CE error codes range from a malfunction of either the drain thermistor, air thermistor, moister sensor, discharge air thermistor, remote control thermistor or the radiant heat sensor, and all the way up to indoor lower louvre limit switch motor.

E0 to E9 error codes range from outdoor activation of outdoor safety device, an outdoor PCB defect, an outdoor compressor motor lock, an outdoor compressor start up error, Outdoor Fan motor lock – Overload up to Outdoor Malfunction of EEV.


F3, F6 and FC error codes.

Error Code Meaning
F3 Outdoor Abnormal discharge pipe temperature
F6 Outdoor Refrigerant overcharged
FC Outdoor Low pressure drop


H3 to H9 error codes starts from a high pressure switch defect, to an outdoor low pressure switch defect, to outdoor current transformer error and finally an outdoor malfunction of air thermistor.

J1 to JH error codes include errors such as Faulty/Fault of pressure sensor, Faulty/Fault of discharge pipe thermistor, Faulty/Fault of suction pipe thermistor, Outdoor Faulty/Fault of liquid pipe thermistor, Outdoor Faulty/Fault of suction pipe pressure sensor and up to Outdoor Faulty/Fault of oil temperature sensor.

L0 to LC outdoor error codes refer to errors ranging from Outdoor Malfunction of inverter, Outdoor Compressor motor grounding short circuit, Outdoor Compressor lock, Outdoor Power unit malfunction and finally up to Outdoor Transmission between inverter and outdoor.

P1, P3, P4 and PJ error codes

Error Code Meaning
P1 Outdoor Inverter over ripple
P3 Outdoor Thermistor abnormality
P4 Outdoor Power unit humidity sensor malfunction
PJ Outdoor Failure of capacity set resistor


U0 to UH error codes refer to system errors ranging from System Shortage of refrigerant or EEV failure, System Wiring check operation not executed, System Transmission between outdoor units, System Transmission error between indoor and central, System Terminals 1 and 3 crossed (Split Skyair) and finally up to System Error with Refrigeration system set up.


Error fault code on Mitsubishi Electric ducted air conditioning systems


Common LG Split System error fault codes



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