Air Conditioner Repair

Step by step repair guide on how to fix an automotive air conditioner. This article pertains to most vehicles.

Difficulty Scale: 3 of 10

Tools and Supplies Needed

  • Air conditioner recharge kit or gauge set
  • Circuit test light
  • Protective eyewear and clothing
  • Flashlight
Begin by parking the car on level ground with the emergency brake set, engine cool.

Step 1 - With the engine "ON" and the AC turned to the coldest setting the compressor should be turning (Note: This can take up to 2 minutes to come on after the engine is started.) (Note: Make sure the serpentine belt is operational.) Inspect the clutch at the front of the compressor, it should be turning "engaged," if so the system has enough refrigerant to activate but if the system is low on refrigerant it will not work properly. In this case an air conditioner recharge kit is needed to recharge the system. 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  (Note: If no air is coming out of the vents, and no blower motor is heard (operating) proceed to step 7.) If the systems state of charge is okay and the compressor clutch is not turning, process to next step.

Compressor Clutch Rotation

Step 2 - If the state of charge is sufficient and the compressor is still not engaging the electrical system must be checked. With the engine and system still "ON" use a test light and check for power at the compressor clutch, If power is present and not turning the clutch coil has failed and must be replaced. (Note: Some compressor engagement coils or non-serviceable and compressor replacement is required.) If no power is observed proceed to the next step.

Step 3 - Using a test light check system fuses located in the PDC (power distribution center) Replace any blown fuse and recheck system. Please visit - Fuse Testing  If fuses check okay, proceed to the next step.

Step 4 - A compressor coil is supplied power from a relay or control unit. Locate and test the relay. Please visit - Relay Testing  Testing a climate controller is a little more difficult and requires a repair manual specific for the car.

Step 5 - An AC system must be able to exchange the heat that is collected from the interior of the passenger compartment. If this cannot be performed the system will not work, or work slightly. The most common cause for this condition is an overheating engine, or a plastic bag has become logged in the vehicles radiator area. Inspect the front of the vehicle and remove any debris. Its also a good idea to use a garden hose and forcing water backward through the radiator area. This will help remove road grime and other debris from the cooling fins of the condenser and radiator. Please visit - Engine Overheating  If everything checks okay, proceed to next step.

Step 6 - The temperature control vents inside a car are controlled by a cable, electric servo or vacuum servo. If the temperature blend door is not functioning properly it will cause warm air from the heater to mix with cold air produced by the air conditioner. To check this start the car and allow the engine idle, turn the blower motor speed on low, switch the temperature control from warm to cold while your ear is close to the vents. An audible noise should heard as the door moves inside the heater box as it swings from open to closed position. If not, inspect for a vacuum leak, shorted servo motor or broken cable.

Step 7 - The air conditioner system utilizes an electric blower motor which forces air throughout the system. If this motor stops working no air will be exhausted from the vents. Please visit - Blower Motor Testing

Helpful Information

When an air conditioner system stops working it basically means one of four things has occurred. The compressor is not working, the system cannot exchange heat, the blend doors inside the climate air control plenum are not working or the blower motor is not working.

Best Practices

  • Service your A/C system about every two years. Activate your air conditioner 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.


Please use our question form if you have a specific question about your car as we are not able to give you a full answer on this page.

Article first published (Updated 2014-12-31)