How to diagnose an air conditioning that is not working

How to diagnose an air conditioning that is not working
How to diagnose an air conditioning that is not working

Driving in hot weather in a car without air conditioning can be uncomfortable and even dangerous in extreme heat. Diagnosing the reason your air conditioning is not working will help you determine if you can fix the problem yourself or if you need to have it fixed. Plus, you'll be less likely to get ripped off if you already know why it doesn't work.


Part 1 of 3: Gather the first information

Diagnose a Non Working Air Conditioning in a Car Step 1

Step 1. Turn on the air conditioning once you are riding

It won't work well if you don't ride. The best position for a diagnostic is the one that gives fresh air (not the one that circulates the air) with the air coming out of the center vents when the air conditioning is on.

  • Start by putting the fan on full power.
  • If your car has a “Max AC” option, select it.

Step 2. Listen carefully

This is to detect unusual noises coming from the air conditioning. Noise may indicate that there is a problem with your compressor and that it needs to be repaired or replaced.

Step 3. Smell the air coming out of the vents

You will need to know if the air is cold, ambient, or warmer than the air around it. Also note if it comes out cold, but then warms up, or if it is overall warm, but blows cold from time to time.

Step 4. Note the air pressure

Set it to full power, then to low and see if the airflow changes as it should.

Step 5. Smell the air coming out of the vents

If there is an unusual smell, there may be a leak. You will probably also need to change the cabin air filter.

Step 6. Inspect your car cables

Look at your car's owner's manual to locate the wiring panel. It can be under the hood, in the trunk, or even in the slot that sits under the driver's feet. A damaged cable can cause an air conditioning unit to stop working.

Part 2 of 3: diagnose airflow problems

Step 1. Check all air outlets

Make sure that the air is expelled from the air outlets you have selected. Move the baffles to see if the air is coming out of the correct outlets.

  • If changing an air outlet doesn't change the airflow, you probably have a problem with the outlet baffle. You will need to replace the deflectors which are in the air outlets and which determine the direction of the air.
  • On some cars, the deflectors close or open when you change the temperature to let more or less air out.
  • Sometimes an air conditioning system that encounters a deflector issue can function normally, but the air is directed elsewhere, for example, to the engine instead of the interior of the car.

Step 2. Look at the cabin air filter

Check the air filter, especially if the air coming out of your vents smells funny or if you think there is a slight decrease in pressure. You will be able to see if there is a buildup of dust or debris.

  • It is possible that your air filter is blocked causing it to interfere with the air pressure and replacing it will be relatively simple and inexpensive.
  • The vehicle owner's manual may contain instructions for changing the air filter. If not, try writing “replace cabin air filter” followed by the year of manufacture and model of your vehicle on the internet (for example, you can search for “replace cabin air filter”. 'passenger compartment for Peugeot 206 from 2005').

Step 3. See if there is a problem with the fan motor

The easiest way to do this is to turn on the heater. If you have minimal airflow when the heater is on, your fan motor may have failed.

  • If the air is only blowing at full power, but not blowing in a weaker position, the fan motor probably has a transistor problem.
  • Unfortunately, mice and other rodents become established in the pipes of HVAC systems and can get stuck in the fan motor when the car is started. A loud noise (and bad smell) that is heard when the heating or air conditioning is on could be a sign of this problem.

Part 3 of 3: diagnose air temperature problems

Step 1. Find the front of your climate condenser

It is usually located in front of the radiator. If there are leaves or other dirt blocking it, remove them and clean the area.

Step 2. Open the hood and find the climate compressor clutch

If the air pressure is normal, but the air is warm, you may have a compressor problem. Look to see if the compressor clutch engages by glancing at it. The compressor is usually located at the front of the engine, right next to the timing belt.

  • The air conditioning must be activated to check the compressor clutch.
  • The compressor looks like a small engine with large wheels at the end. The wheel (which is the compressor clutch) should turn. If not, you have a compressor problem.

Step 3. Check the tension on the compressor belt

It must be tense. If it's loose, you need a new compressor belt.

Step 4. Check for any refrigerant leaks

One of the most common air conditioning temperature concerns is the low amount of coolant. The air conditioning system is closed, so fluid cannot be lost unless there is a leak.

  • Look for oily residue on or around the pipes that connect the air conditioning components to each other. Oil stains can indicate a leak.
  • You may want to consider using an electronic leak detector: it can spot very small amounts of coolant.
  • Some testers use dye, ultraviolet light, and protective glasses to find leaks.
  • If you find any, you will likely need to hire a professional to fix them. You will also need new hardware, as many components cannot be repaired.

Step 5. See if the system hangs

If your air conditioning blows cold air initially, then shuts off after a while, it may be blocked. Excess air and moisture in the system can cause components to jam.

  • A saturated accumulator or receiver can cause a blockage.
  • Turning off the system for a while and letting it unlock will resolve the issue temporarily.
  • If the problem persists, you will need to flush your system using a pump.


  • Do not add coolant unless you are sure that its small amount is the cause of the problem, as too much can seriously damage your system.
  • It is always better to consult a professional to make repairs on your vehicle.
  • Wear protective glasses and work outdoors or in an open area where the fumes will not make you sick. Never touch your eyes or mouth after handling Freon or other chemicals. Wear long sleeves and gloves whenever possible.

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