From the magazine: Car AC not blowing cold air: Diagnoses and fixes – Auto Service World

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Having an AC that won’t blow cold air is frustrating in summer’s heat. Find out how to diagnose and fix a car with this issue in a few steps
A car AC not blowing cold air is one of the most common problems a driver will face. Some ACs blow warm air while others blow moderately cool air. Either way, the driver’s dealing with a malfunctioning AC.
A clogged filter, bad AC compressor or refrigerant leaks could be the problem. Hence, instead tolerating an uncomfortable car, it’s best to diagnose the issue and find a fix for your customer. Let’s go through the easiest methods of diagnosing a car AC that’s blowing warm air so you can repair it properly.
You could even save time and their money if you can figure out the proper fix.
Cooling Fan Problems
Vehicles use cooling fans to move cold air into the cabin. If you’ve set the air conditioning to the max and the fans are on the high setting, but the air is moderately cool, the cooling fans could be the culprit.
A vehicle has two cooling fans — one is the AC condenser fan, and the other is the radiator fan.
Here are some of the symptoms of a bad AC condenser fan:
How do you diagnose a bad condenser fan? The condenser fan spins immediately after you turn on the AC. Locate this fan under the hood as it sits next to the radiator fan. Then, have someone turn on the AC and observe if it starts to spin.
If it does not begin to spin, you may want to identify the cause, as it could be a failed fan relay, blown-fuse, failed temp sensor, damaged wiring, or the ECU not commanding it to turn on.
To fix, you will need to fix the problem according to the cause. For example, a blown-fuse or wiring issue should be easy to do at home. In addition, you may need to change a faulty temperature sensor as it could be preventing the fan from coming on when it doesn’t relay the turn-on message to the ECU.
An auto mechanic can identify and fix all these problems, and most condenser fan problems don’t cost more than a few hundred dollars to fix.
The radiator fan cycles on and off with the engine warmed up or idling. Some of the symptoms of a failing radiator fan include:
Diagnose by locating the radiator fan on the radiator. Next, turn on the vehicle and let it get warm. Then, observe if the radiator fan starts to spin when the vehicle becomes warm. A radiator fan that does not spin could be a problem with the fan itself or its motor.
To fix, it’s always best for a technician to look at the radiator fan to determine the cause of the problem. Replacing a radiator fan costs between $550 to $650, while the radiator fan itself will cost around $400 to $450.
A bad AC compressor
The car’s AC is dependent on the compressor to keep the air circulating. If the compressor is in bad shape, the refrigerant will not move around and the AC will not produce cold air.
Here are some of the symptoms of a bad AC compressor:
After you notice signs of a bad compressor, the next thing will be to diagnose it.
After concluding that the problem causing the AC to blow warm air is a bad air compressor, the best thing is to replace it. Consider replacing the O-rings, the accumulator, and the expansion device when replacing it.
Refrigerant Leak
The AC system is filled with refrigerant to work correctly. This refrigerant starts as a gas on the low-pressure side and is converted into a liquid on the high-pressure side. It’s this process that keeps the cabin cool when the AC is on.
Over time, leaks develop in the system, and the refrigerant level drops.
Here are some of the symptoms of refrigerant leaks:
It’s time to recharge the system, especially if you’ve never refilled it in the last six or seven years. Unfortunately, vehicle owners can’t recharge their AC at home because refrigerant needs proper handling by a licensed technician. Also look for leaks if the cause of the low refrigerant is a leak in the system.
Clogged or dirty filter
The AC filter removes contaminants from the air entering the vehicle’s air conditioning system. It removes impurities, allergens, and pollutants that make the cabin uncomfortable.
A cabin filter will become dirty and clogged over time. When it’s excessively dirty, it will show some symptoms such as:
To fix, there’s no way around a clogged or dirty air filter except to replace it. A standard particulate air filter needs replacing after every 50,000 km, while an activated charcoal cabin air filter should be replaced after 25,000 km or once a year.
Fixing the problem if a car’s AC not blowing cold air is not always easy. Remember, you can always check the car’s manual.
This article originally appeared in the July/August 2022 issue of CARS magazine
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