Troubleshooting a Car Air Conditioner That Won't Turn On

A female hand adjusting the vent on a car dashboard.

Troubleshooting a car's air conditioner is an important part of knowing your car, and can be a real life-saver in the summer heat. When your air conditioner won’t work, put on your DIY hat, take a look at the system, and try to figure out what’s wrong. This will save you time and money with a mechanic, and could make it possible for you to fix the problem yourself.

How Your AC Works

It’s impossible to troubleshoot problems with your air conditioning if you don’t know much about how it works. Air conditioning is actually less complex than you may think. The system is made up of a compressor that pumps Freon (a gas and liquid combination) through the entire system.

The Freon goes through expansion valves where the gas/liquid combination expands or contracts based on how much air conditioning is needed. The cold Freon then goes through an evaporating core, where the cold air it creates is released into the car.

Check Your Front

If your air conditioner refuses to work, check for the simplest problems first to save yourself some time. Get out of the car and look all around your front grill and bumper. Pieces of debris and mud can hinder airflow under the hood of the car, which will prevent your AC from working. If you see anything that could be restricting air flow, get it out of there and try the AC again.

Take a Look at the Belt

With the car turned off, open your hood and take a look at your AC system. The air conditioner compressor itself will have a belt around it. Check the belt to see if it's loose or missing. Fix it or have it fixed if you find any problems with the belt, and this should solve your AC problem.

Make Sure the Compressor Works

A car air compressor against a white background.

Check to see if the air conditioning compressor is still working if you can’t find any obvious issues. Leave your car's hood open and turn on the engine. Turn on your AC even if it isn't working, and go to the front of your car to listen to the compressor. You should hear the AC compressor working or attempting to work.

If it's silent, you may have a fuse that has burnt out or disconnected. The wiring leading to and from the compressor could also be damaged or worn away. Have a mechanic check over the electrical system for the compressor, and this could put your AC back in business.

Test Your Fan

Make sure that the fan is working when the AC is turned on. If you do not hear a motor running when you turn on your air conditioner, you may have a fan problem. No noise could mean the fan’s motor is stalling or has already died out. Has your AC airflow been decreasing recently? This is often a warning sign that the fan’s motor is wearing out. Replace the fan to give your AC the power it needs.

Look for Leaks

The air conditioning system is put together with several fittings and seals, which are potential weak points that can corrode and wear away over time. This may leave small holes and cracks in the system that causes leaks.

This will make your AC system lose Freon so cooled air flow is noticeably warmer. Use a leak detector around your A/C hoses and compressor to see if this is your problem. If you believe your system is leaking, take it to a mechanic to get it resealed and have the hoses replaced.

Low Freon Levels

A mechanic working on a car.

Can’t figure out what's wrong with your air conditioner? It’s likely that your Freon level is low. You’ll need to have the Freon filled or the AC recharged by a qualified mechanic.

Be sure to ask the mechanic to check for Freon leaks while he’s refilling or recharging the system because you don’t want the AC to stop working again in a month. If you use your air conditioner frequently, you should only have to refill your Freon or recharge your AC once a year at most.

DIY Troubleshooting

Learn how to troubleshoot your own air conditioner problems, and you could save a lot of frustration and money. You may even find a simple DIY solution to get your air flow going again and get back on the road. Get to know your own AC system, and you’ll find out that it’s not as complex as you think it is.