A Guide to Air Conditioner Fault Codes

It’s Saturday, it’s hot, and the worst happens – your air conditioner fails. An error code keeps popping up, and the manual you swore you’d keep handy is nowhere to be found.

Don’t panic – we have a guide to air conditioner fault codes to help you! We will explore some standard fault codes across the most popular brands of air conditioner units so you can work out what’s wrong – and fast!

The importance of air conditioning maintenance

Regular air conditioner unit maintenance won’t stop error messages from popping up entirely. That said, they can help minimise how often you’ll see them – and how serious they turn out to be!

Simple maintenance tasks that you can perform yourself include:

Cleaning or replacing filters
Making sure filters are secure
Cleaning the evaporator coils
Cleaning the unit casing
Checking window seals in air-conditioned rooms
Booking a service for your unit

To help you, check out our blog for great advice and suggestions. Start with our guide to fixing a musty air conditioner or booking a split-system service.

Air conditioning fault codes for different brands

Fault codes will vary from brand to brand, so we’ve covered some of the most popular here. You might also find that codes will differ depending on your model, so keep your manual handy to double-check. If you’ve lost yours, you may be able to find PDF copies online through your chosen brand’s website.

Please note that these fault codes relate to indoor units only.

Daikin air conditioning fault codes

Code	Description	Cause
A0	External protection device activated.	The external protection device connected to the terminal strip T1-T2 of the indoor unit is activated.
A1	Malfunction of the indoor unit PCB (Printed Circuit Board).	Defective indoor unit PCB.
A3	Drain level control system abnormality.	Drain clogging, upward slope etc. Defective drain pump. Defective float switch or short circuit connector.
A4	Malfunction of freezing protection.	Shortage of water volume. Low water temperature setting. Defective water temperature thermistor.
A5	High-pressure control in heating, freeze-up protection control in cooling.	Clogged air filter of the indoor unit and short circuit defect of indoor unit heat exchanger thermistor.
A6	Malfunction of the fan motor.	Broken wires in, short circuit of or disconnection of connectors from the fan motor harness. Defective indoor unit PCB. Defective fan motor.
A7	Malfunction of swing flap motor.	Defective swing flap motor. Defective indoor unit PCB. Defective connection cable. Defective airflow direction adjusting flap-cam.
A8	Malfunction of power supply or AC input overcurrent.	Defective power supply voltage. Defective connection on signal line. Defective wiring.
A9	Malfunction of electronic expansion valve.	Defective electronic expansion valve coil. Defective indoor unit PCB. Defective relay cables.
AA	Heater overheat.	26WH is activated.
AF	Malfunction of a humidifier system.	Humidifier unit (optional accessory) leaking. Defective drain piping (upward slope etc.) Defective indoor unit PCB.
AH	Malfunction of the dust collector of the air cleaner.	Defect of dust collecting element. Stained insulator part. Defect of high voltage power supply unit. Defect of indoor unit PCB.
AJ	Malfunction of capacity setting (indoor unit PCB).	The capacity setting adaptor was not installed when replacing PCB. Defective indoor unit PCB.
C1	Failure of transmission (between indoor unit PCB and sub-PCB)	Defective connection of the connector between indoor unit PCB.
C4	Malfunction of liquid pipe thermistor for heat exchanger.	Defective thermistor for liquid pipe. Defective indoor unit PCB. Defective connector contact.
C5	Malfunction of gas pipe thermistor for heat exchanger.	Defective thermistor for gas pipe. Defective indoor unit PCB. Defective connector contact.
C6	Malfunction of fan motor sensor or fan control driver.	Defective fan PCB. Defective connection of capacity setting adaptor Field setting error.
C7	Front panel driving motor fault.	Defective front panel driving motor. Defective limit switch.
C9	Malfunction of suction air thermistor.	Defective thermistor for suction air. Defective indoor unit PCB. Defective connector contact.
CA	Malfunction of discharge air thermistor.	Defective thermistor for discharge air. Defective indoor unit PCB. Defective connector contact.
CC	Malfunction of humidity sensor system.	Defective humidity sensor. Defective connector contact.
CJ	Room temperature thermistor in remote controller abnormality.	Defective room temperature thermistor in the remote controller. Defective remote controller PCB. External factors (noise etc.)

Panasonic air conditioning fault codes

Code	Description	Cause
H11	Indoor/outdoor abnormal communication.	Either the control cards are not working properly, or there is no connection between the internal and external modules. If this fault surfaced right away following the installation of the air conditioner, there were mistakes in the main line. It is time to replace the board if the issue started to occur after the air conditioner has been operating for a few years. It is imperative to determine whether the exterior or internal unit failed. The indoor unit fan may keep running in the event of an error.
H12	Other power errors between the outdoor and indoor units.	The total power of the internal modules does not match the power of the external. Such an error appears only in multi-splits. The signal appears 1.5 minutes after switching on. There can be 3 options: 1. Incorrectly calculated cooling capacity of indoor units. 2. The number of internal modules is incorrectly selected – the external unit cannot cope. 3. Error H11 appeared on one of the blocks, and then H12 appeared on the other (the wrong number of internal modules).
H14	Room temperature sensor error.	The air sensor isn’t working properly; it records room temperatures that are either +46ºC or -56ºC. This indicates a short circuit in the sensor or a break in the circuit.
H16	Compressor load current is too low.	The external module detects low current consumption. Here are 3 reasons why a drop in consumption can happen: 1. not enough freon (low pressure); 2. current transformer defect (it is necessary to solder or replace the board); 3. failure of the power IPM module.
H17	Similar to H14.	Comparable to H14, but pertaining to the exterior unit: a malfunction of the compressor’s suction pipe’s temperature sensor. On the sensor, there has either been an open circuit or a short circuit.
H19	Motor mechanism of indoor fan is locked.	When the internal module motor’s real speed deviates from the speed that the processor specified, an error message appears, signalling that the module motor is jammed. Here are some reasons for these errors: 1. Problems directly with the motor of the indoor unit 2. The connectors of the wires of the engine of the indoor unit were loosened 3. Problems with the internal module board.
H21	Drainage blocked or float sensor defective.	The indoor unit’s drain pan float was having issues. The sensor is open when there is a signal. It is necessary to examine the sensor logic and measure the resistance on the pump’s motor windings, which ought to be around 200 ohms. Additionally, drainage may block; therefore, cleansing the drainage system is necessary.
H23	Indoor heat exchanger temperature sensor abnormality.	Issues with the heat exchanger’s base sensor No. 1 for surface temperature in the interior unit. When the temperature of the heat exchanger falls below -40º or rises over +80ºC, the CPU identifies this anomaly. You must check for either a short circuit on the sensor or an open in the circuit.
H25	Defective ionisation unit or internal board.	The ionisation unit is having issues. When the E-Ion is off, the port is on. The internal module board or the E-Ion board might be having issues.
H27	Outdoor intake air temperature sensor abnormality.	The air temperature sensor is having issues. The processor logs the outside temperature when it is higher than +150ºC or lower than -40º. An open circuit or a short circuit on the sensor might be the root of the problem.
H28	Outdoor heat exchanger temperature sensor abnormality.	Issues with the outside unit’s heat exchanger’s sensor No. 1 measuring surface temperature. The heat exchanger’s surface temperature is fixed by the processor at +110ºC or -60ºΡ. Either an open circuit in the circuit or a short circuit in the sensor is the source of the issue.
H30	Outdoor discharge air temperature sensor abnormality.	Issues with the compressor’s discharge pipe’s temperature sensor. Temperature measurements over +200ºC or below -16ºΡ are recorded by the processor. When the condensation temperature is six degrees greater than the discharge temperature, an open in the temperature sensor’s circuit is identified. A short circuit or open circuit on the sensor might be the source.
H33	Indoor/outdoor wrong connection.	When there is a voltage imbalance in the data transmission line between the internal and external modules, an interconnect problem manifests itself. The interior and or outdoor units’ electrical lines are having issues.
H34	Outdoor heat sink temperature sensor abnormality.	The temperature sensor that is mounted in the power module’s radiator has malfunctioned. The processor measures the temperature difference between the external unit’s heat exchanger plates at +80ºC and -43ºC. Either the circuit was open, or the sensor had a short circuit.
H36	Outdoor unit gas tube temperature sensor is closed/torn off.	When the external module was in heat mode, there were issues with the temperature sensor in the gas tube. The temperature over + 149ºC or below -45ºC is recorded by the processor. Inspect the sensor or circuit for any short circuits.
H37	Outdoor unit liquid tube temperature sensor short-circuited.	There were issues with the outdoor unit’s liquid tube temperature sensor when it was in the cold setting. On the sensor, there has either been an open circuit or a short circuit.
H39	Abnormal indoor operating unit or standby units.	The indoor unit is in standby mode and has frozen. arises as a result of an unusual unit evaporator temperature. All blocks show this signal at the same time, with the exception of the block where the evaporator is freezing. On the final block, an error number F17 is shown.
H41	Incorrect wiring and freon wiring.	Inconsistency in the connection of wires and freon conduits.
H64	Malfunction of the high-pressure sensor.	The high-pressure sensor that is mounted in the outside unit isn’t working properly. When the compressor is turned off, the high-pressure sensor stays open for a minute. Possible causes of the failure include damage to the sensor itself, broken wires, or issues with the board’s connections.
H97	Faulty compressor motor, indoor unit board.	The external unit’s engine gets stuck because it runs faster than the CPU has programmed it to. Reasons for these failures – Damage to the motor of the external unit Breakdown of the internal module board Problems with the connectors of the wires.
H98	Protection for total current consumption.	The internal module’s defence against high pressure or overheating when in heat mode has been effective. Protection kicks in when the heat exchanger in the interior module reaches + 52 °C, and the compressor shuts off entirely when the temperature reaches + 65 °C. When the temperature lowers, the compressor resumes.
H99	Error of the DC protection system.	Possible causes are jamming of the compressor, failure of the transistor module, malfunction of the current sensor of the board of the external unit, the resistance of the compressor windings is below normal.
F11	Incorrect operation of the four-way valve.	This error suggests that the 4-way valve in charge of the heat/cold switching is not operating correctly. Its mechanism or the electromagnetic valve coil may be defective.
F17	Freezing of the indoor unit.	Freezing of the indoor unit in standby mode, an error appears on the unit on which the fact of freezing is detected.
F90	Open circuit of compressor windings.	The signal appears when – When the compressor windings break (each winding under normal conditions should have a resistance of about one Ohm); If there is a difference in the resistance of the windings; If a malfunction occurs in the inverter circuit of the outdoor unit board. To eliminate the malfunction, measure the resistance and voltage.
F91	Incorrect operation of the refrigeration circuit.	The error indicates that the low-pressure protection in the refrigeration circuit is activated or that it is operating incorrectly.
F93	Open compressor windings, inverter board malfunction.	The signal shows a discrepancy between the controller control signals and the compressor’s actual performance. Stated differently, when its velocity deviates from the controller’s control signals. Here, the system shuts off.
F94	Overpressure protection.	Excessively high discharge pressure initiates protection. The refrigeration circuit’s functionality must be examined.
F97	High compressor discharge temperature.	The compressor overheats due to its set high discharge temperature. After 20 minutes of uptime, the problem could reset itself. Frequent shutdowns of the external module without obvious cause are one indicator of a problem.
F99	Error of the DC protection system.	Possible causes are jamming of the compressor, failure of the transistor module, malfunction of the current sensor of the board of the external unit, the resistance of the compressor windings is below normal.

Samsung air conditioning fault codes

Samsung divides its error codes into ones that can be fixed at home and ones that require a technician to assess and repair.

Here’s the ones you should be able to manage yourself:

Code	Description	Cause
CF	Filter cleaning reminder or filter reset indicator.	Clean or replace the inner filters of the indoor unit. Then, remove the filter cleaning reminder using the air conditioner’s remote control. (Refer to the user manual if needed.)
CI	The Auto clean function (this function starts immediately when the AC is off).	This indicates that the Auto clean function has been enabled. You can turn off this function using the air conditioner’s remote control. (Refer to the user manual if needed.)
dF	Auto Defrost function (during the defrost operation).	This indicates that the Auto Defrost function has been enabled. This is not a product defect, but one of the modes used during heat operation to protect the outdoor unit.

And here’s the ones for the professionals:

Code	Description
C1 or 21 on loop	Defective room temperature sensor error.
C1 or 22 on loop	Defective heat exchanger temperature sensor.
C1 or 54 on loop	Fan is not rotating.
C1 or 63 on loop	Incorrect or deleted data of EEPROM for main control board.

Mitsubishi air conditioning fault codes

Unlike the other major brands, Mitsubishi does not provide a detailed cause for the error or a suggested solution.

P1	Intake sensor error.
P2/P9	Pipe (Liquid or 2-phase pipe) sensor error.
E6/E7	Indoor/outdoor unit communication error.
P4	Drain sensor error.
P5	Drain pump error.
PA	Forced compressor error.
P6	Freezing/overheating safeguard operation.
EE	Communication error between indoor and outdoor units.
P8	Pipe temperature error.
E4	Remote controller signal receiving error.
Fb	Indoor unit control system error (memory error, etc.).
E0/E3	Remote controller transmission error.
E1/E2	Remote controller control board error.
E9	Indoor/outdoor unit communication error (Transmitting error) (Outdoor unit).
UP	Compressor overcurrent interruption.
U3/U4	Open/short of outdoor unit thermistors.
UF	Compressor overcurrent interruption (when compressor locked).

Master reset

That old IT adage “Have you tried turning it off and on again?” doesn’t just apply to computers! Sometimes, a master reset of your air conditioner can help fix any fault codes, at least temporarily.

A master reset turns off the electrical switchboard of the air conditioner, wiping the “memory” of the functions the unit was performing before the reset.

Because a master reset won’t actually address any of the issues that may have caused a fault code to display, we recommend using this when a repair technician is unavailable, such as a weekend or public holiday.

Be sure to note the displayed fault codes so you can pass them on to a professional as soon as one is available to assess your unit.

How to perform a master reset

First, locate your air conditioner’s outdoor unit.
Somewhere on the unit or the wall beside will be a large on/off switch. This is the isolator switch.
Turn the switch to the off position and leave for one hour.
Turn the switch back to the on position.
Assess how the system is running and make note of any displayed error codes.

Due for a service?

The best way to manage those pesky fault codes is to keep up with your maintenance requirements and schedule regular services. Contact our team to book a service or to have one of our team take a look at a fault code and get yourself set for the summer!