Driving on a hot day in a car where the air conditioner is not working can be uncomfortable and even dangerous in extreme heat. Diagnosing the cause of a malfunctioning air conditioner will help you decide whether the problem can be fixed yourself or needs to be taken to a repair shop. You're also less likely to be used in the workshop if you already know the cause of the air conditioner not working.
Step
Method 1 of 3: Gathering Initial Information
Step 1. Turn on the air conditioner when the car is running
Air conditioning will not work properly unless the engine is running. The best setting for diagnosing is “fresh air” (not recirculated) with the wind blowing from the center air vent on the dashboard and the air conditioner turned on.
- Start with the fan speed on the highest setting.
- If your car has a setting of “Max AC (max air conditioning)”, select that option.
Step 2. Listen for unusual noise from the air conditioner
Noise can indicate a problem with the compressor and that the compressor needs to be repaired or replaced.
Step 3. Feel the air coming out of the vent
You need to know if the air is cold, has room temperature, or is hotter than the surrounding air. Also notice if it's cold at first but turns warmer, or if it's usually warm but cools off intermittently.
Step 4. Pay attention to the air pressure
Turn the air pressure on to the high and low settings and see if the airflow changes as it should,
Step 5. Smell the wind coming out of the air outlet
If there is an unusual odor, there could be a leak. You may also need to replace the cabin air filter.
Step 6. Check your car fuse
Refer to the owner's manual for the location of your car's fuse panel, as it could be under the hood, in the trunk, or even in the driver's foot area. A blown fuse can cause your air conditioner to stop working.
Method 2 of 3: Diagnosing Airflow Problems
Step 1. Check all vents
Make sure the air pressure comes out of the selected vent. Move the vent selector to see if air is moving into the correct vent.
- If changing the vent doesn't change the airflow, you may have a problem with the blend door (the door that alternates the flow of hot and cold air in the air conditioning and heating system), which requires you to replace the door in the dashboard that determines the direction of airflow.
- The blend door changes position when the temperature selection changes, blocking or allowing the flow of both hot and cold air.
- Sometimes an air conditioning system with a faulty door mode may work properly, but the airflow is directed elsewhere, such as back into the engine, instead of into the car.
Step 2. Pay attention to the cabin air filter
Check the air filter, especially if the air coming out of the vent smells strange or if you feel a slow drop in pressure for some time. You will be able to see if there are lumps of dust or debris inside.
- There is a possibility that the cabin air filter is clogged so that it interferes with air pressure. Replacing it is a relatively easy and inexpensive solution to the problem.
- Your car's manual may contain instructions for replacing the cabin filter. If it's not there, try searching the internet for “replace cabin air filter” followed by the year, manufacturer, and model of your car (for example, you might be able to search for “replace cabin air filter 2006 Toyota Camry”).
Step 3. Check for blower motor problems
The easiest way to do this is to turn on the air heater. If the airflow is also weak when the heater is on, the blower motor may have been damaged.
- Blower motors can have resistor problems if air is blowing only at the high setting but not blowing at the lower setting.
- Unfortunately, rats and other rodents sometimes make nests in a car's HVAC hose and can get caught in the blower motor when the car is started. Loud noises (or unpleasant odors) that occur when the heater or air conditioner is turned on can be a sign of this problem.
Method 3 of 3: Diagnosing Air Temperature Problems
Step 1. Locate the front of the air conditioning condenser
Usually located in front of the radiator. If leaves or other debris get in the way, remove and clean the area.
Step 2. Look under the hood on the air conditioning compressor clutch
If the air pressure is normal but the air is hot, you may have a compressor problem. Checking that the compressor clutch is installed is a simple visual inspection. The compressor is usually located at the front of the engine, inside the grille of your car.
- Make sure the car is running and the air conditioner is on to check the compressor clutch.
- The compressor looks like a small motor with a big wheel at the end. The wheel (which is the compressor clutch) must turn. If it doesn't spin, you have a problem with the compressor.
Step 3. Check compressor belt pressure
The pressure must be tight. If it's loose, you'll need a new compressor belt.
Step 4. Look for any cooling system leaks
One of the most common causes of air conditioning temperature problems is a small amount of refrigerant. The air conditioner has a closed system, therefore the refrigerant should not be reduced unless there is a leak.
- Look for oily residue on the surface or around the hoses that connect the air conditioning components together. Oily stains may indicate a refrigerant leak.
- You might consider using an electronic leak detector, which can detect a smaller amount of refrigerant.
- There are several test kits that use dye, UV light, and protective goggles to find leaks.
- If you find a leak, it's likely that you will need to hire an expert to fix it. You may also need new parts, as many components cannot be repaired or patched.
Step 5. Check for freezes
If the air conditioner is intermittently blowing cold but then no longer cools after a few uses, there may be a freeze. Excess air and moisture in the system can cause components to freeze (literally).
- Freezing can also be caused by the reservoir/dryer or the accumulator being saturated.
- Temporarily shutting down the system and letting it thaw out will temporarily solve the problem.
- If the problem doesn't go away, you may need to drain the system or evacuate using a suction pump.
Warning
- Do not add refrigerant unless you believe a lack of refrigerant is causing the problem, as filling the system with excess refrigerant can cause severe damage.
- It is always a good thing to consult an expert to make repairs to your vehicle.
- Wear safety glasses and work outdoors, where the smell won't bother you. Never touch your eyes or mouth after handling freon or other chemicals. Wear long sleeves and gloves whenever possible.
