Air Conditioner Troubleshooting

Easy step by step guide on how to troubleshoot an automotive air conditioner, though appearances may vary the process is the same, problems are listed in order of popularity, this article pertains to most vehicles.

Difficulty Scale: 5 of 10

Begin by parking your car on level ground with the emergency brake set, engine cool, wear safety eyewear and gloves.

Step 1 - Using a test light check the A/C system fuses located in the PDC (power distribution center) replace any blown fuses and recheck. Please visit - Fuse Testing

Test Fuses

Step 2 - With the engine "ON" and the A/C turned to the coldest setting with high fan speed the compressor should be operating, on older models a clutch is used to engage the compressor which is easy to see. (Note: This can take up to 1 minute to come on after the engine is started.) If the system is low on refrigerant it could cycle on and off, making a ticking noise. If the compressor clutch doesn't engage attach a pressure gauge or recharge kit to the low pressure side port to inspect system pressure readings. Please visit - AC System Recharge

Compressor Clutch Rotating

On newer models an internal compressor valve is actuated which activates the pump, a gauge set is used to determine if the compressor is working. Please visit - AC System Recharge

Air Conditioner Gauge Set

Step 3 - If the level of refrigerant is low in the system it will not cool sufficiently. Please visit - AC System Recharge

A/C Recharge Kit

Step 4 - If the state of charge is sufficient and the compressor will still not engage, the electrical system must be checked. With the engine and system still "ON" use a test light and check for power at the compressor, if power is present and the compressor is not working replacement is needed. If no power is observed proceed to the next step.

Air Conditioner Compressor

Step 5 - Trigger power to the compressor is supplied by a relay or control unit, locate and test the relay, testing a climate controller is a little more difficult and requires a wiring diagram. Please visit - Relay Testing

Testing Air Conditioner Relay

Step 6 - The A/C system must be able to exchange the heat at the condenser or the system will not work, or work poorly, the most common cause for this condition is engine overheating which can be caused by a plastic bag lodged in the condenser. It's also a good idea to use a garden hose to force water backward through the radiator area, this will help remove road grime from the cooling fins of the condenser and radiator. Please visit - Engine Overheating

Coolant Leak

Step 7 - If a temperature blend door actuator is not functioning properly it will cause warm air from the heater to mix with cold air from the air conditioner. Start your car and allow the engine idle, turn the blower motor speed on low speed, switch the temperature control from warm to cold while your ear is close to a dash vent. An audible noise should be heard as the door moves inside the heater box from open to closed position. If not, suspect a shorted servo actuator motor or a vacuum leak on older vehicles. Please visit - Bend Door Actuator Replacement

Blend Door Actuator

Step 8 - An electric blower motor forces air throughout the ventilation system, if this motor stops working no air will be exhausted from the vents. Please visit - Blower Motor Testing

Blower Motor

Step 9 - Most vehicles are equipped with a cabin air filter which can clog causing the air flow to be restricted or stop. Please visit - Cabin Air Filter Replacement

Replacing Cabin Air Filter

Best Practices

  • Service your A/C system about every three years, activate the system periodically to keep components lubricated.



Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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