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Peak Performance: Basic Car AC Check For Comfortable Cruising

car AC check

Car air conditioning systems can be used in all seasons — in winter and during rain storms to defog the windshield and in summer to cool you off — but there’s no doubt that summer is when most car air conditioning systems are truly put to the test. Failing the test will invariably leave you sweaty, uncomfortable and irritable. Summer is officially here, and if you haven’t checked out your air conditioner yet, then right now is a good time. While we can’t get into actual diagnosis and repair, as the tools and training required are strictly professional level, there are a few car AC check points you can do yourself if your car air conditioning isn’t working right.

One of the first things you can do is grab a thermometer and stick it in an air vent; a cooking thermometer might work if it ranges between zero and 100 degrees Fahrenheit. With the windows closed, the climate control system set to full recirculation, the fan on high and the engine at 1,500 or 2,000 rpm, air vent temperature should be 30 to 45 F lower than the temperature outside. In other words, if everything is working right, and it’s 90 F outside, then air vent temperature should range from 45 to 60 F. A higher temperature might indicate a problem with your car air conditioner. Before you take it to the professionals, here’s how to check the basics.

A Loose Drive Belt Could Lead to Car Air Conditioning ProblemsBasic Car Air Conditioning Checks

On most cars, the air conditioner compressor is run by a V-belt or serpentine belt. If the belt is slipping, you’ll probably hear some squeaking or squealing noise. A slipping belt also won’t drive the compressor reliably.

If the compressor clutch isn’t cycling — not all compressors have clutches — then check the compressor clutch fuses, relays and connections. Low refrigerant pressure can also prevent compressor operation, but this issue requires professional diagnosis and repair.

On vehicles with electric radiator fans, the fans should run whenever the compressor engages. If not, check fuses, relays and connections.

Keeping Clean and Cool

Air conditioner performance depends on air flow to pump heat out of the cabin. Anything that impedes the air flow in the cabin, whether through the condenser, in front of the radiator or through the evaporator, can reduce air conditioner efficiency.

Through the grille, use a pressure washer or garden hose to wash out dirt, grime, leaves or bugs that are blocking air flow. A clean condenser will release heat more readily into the atmosphere.

It’s also a good idea to check the cabin air inlet for blockage. It’s usually located near the windshield cowling. Clean out any leaves or debris that may be blocking air flow into the cabin.

After months of collecting dirt, dust, pollen and bugs, the cabin air filter tends to fill up, slowing the flow of air and damping air conditioner performance. A clogged cabin air filter might also give off an unpleasant odor, letting you know that you’re past due to replace it.

Finally, an overheating engine can lead to an overheating cabin. Be sure that fan shrouds, air dams and the engine cooling system are installed and working properly.

Part of being a good DIY mechanic is recognizing limitations. If you don’t have the tools, training or experience to go deeper into car air conditioning diagnosis and repair, then consult your local NAPA AutoCare Center, and your ride will be cool in no time.

Check out all the air conditioning system parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on performing a car AC check,, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Max Pixel.


Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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