How to Find the Cause of Car Air Conditioner Not Working

Driving a car on a hot day without air conditioning will make you uncomfortable, even dangerous if the weather is too hot. If you want to know if you can fix the air conditioner yourself or have to take your car to a service shop, first you need to find out what’s causing it to not work. You also avoid the risk of being taken advantage of by a mechanic if you have found the reason why the air conditioner is not working.

Table of Contents

Initial information gathering

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Turn on the air conditioner while the car is running. The air conditioner will not work properly unless the engine is running. To determine the exact cause, you must turn on the air conditioner and set the “fresh air” mode (fresh air, not recirculation), then the air will blow out from the middle slots.

Start setting the fan speed to the highest setting.
If the vehicle has a “Max AC” setting (maximum cold), select that.

Listen for unusual noises coming from the air conditioner. The noise indicates that the air compressor has a problem and needs to be repaired or replaced.

Feel the air blowing out of the vent. You need to distinguish whether the air temperature is cold, equal to room temperature or hotter than the surrounding air. Also watch out for cases where the fresh air that blows out is cold but then gets warmer, or it’s consistently warm but sometimes gets cold.

Pay attention to the air pressure. Adjust the air pressure to high and low, paying attention to whether the airflow changes as usual.

Smell the air blowing out of the vent. If there is an unusual smell, the air conditioner may have a leak. You may also have to change the cockpit air filter. ^{[1] X Research Source}

Check the vehicle’s fuse. Check your vehicle’s owner’s manual to locate the fuse panel, as it may be under the bonnet, in the trunk, or under the driver’s footrest. A blown fuse can cause the air conditioner to fail.

Diagnosing air flow problems

Check all air vents. Make sure the air is coming out from the vents you have selected. Change to another air vent to see if the air is blowing out the correct slit.

If changing the vents doesn’t change the airflow then the mixing door may be malfunctioning, you need to replace the mix door inside the vents because that’s the part that determines the direction the air is coming out. ^{[2] X Research Sources}^{[3] X Research Sources}
The mixing doors change position as you change the temperature, blocking or allowing hot or cold air to blow out.
Sometimes the air conditioner has a problem with the mixing door, but it can still work fine, but the air flow is directed elsewhere, like blowing back out of the engine instead of blowing into the car.

Diagnosing problems at air temperature

Find the location of the air conditioner heater. It is usually located in front of the radiator. If there are leaves, dirt, or other obstructions in the outdoor unit, clean the area.

Look under the bonnet at the air compressor clutch position. If the air pressure is normal but the air is hot, the car may have a problem with the air compressor. Simple visual check to see if the compressor clutch is closed. The compressor is usually located in front of the car engine, right inside the car’s grille.

You must start the car and turn on the air conditioner to check the compressor clutch.
The air compressor looks like a small motor with a large wheel at one end. That wheel (which is the compressor clutch) must be spinning. If it doesn’t rotate then the compressor has a problem. ^{[6] X Research Source}

Check the belt tension of the air compressor. The belt must be tight enough. If it is loose then you need to replace the wire with a new one.

Look for signs of refrigerant leaks. One of the most common causes of temperature problems is a lack of refrigerant. The air conditioner is a closed system, so refrigerant cannot be lost unless there is a leak. ^{[7] X Research Sources}

Look for oily deposits on or around the ducts that connect the air conditioning system. Greasy deposits are a sign of refrigerant leaks.
An electronic leak detector is recommended as it can detect very small amounts of refrigerant escaping.
In addition, there are some devices that use dyes, ultraviolet light, and protective glasses to locate leaks.
If you find a leak, you’ll have to hire a plumber to seal it up. You may need to replace some parts, as many cannot be repaired or soldered.

Check for freezing. If the air conditioner blows cold air at first but then stops being cold, it may have frozen. Excess air and moisture in the system can cause components to freeze (literally). ^{[8] X Research Sources}

Freezing also occurs when the separator is oversaturated.
Turning off the air conditioner for a while to let the ice melt is a temporary solution to the problem.
If the problem persists then you must pump air to clean the air conditioning system with a vacuum pump.

Warning

Do not pump more refrigerant unless you are sure it is due to a shortage of refrigerant, as an air conditioning system with excess refrigerant can cause serious damage.
The best way is always to hire a mechanic.
Wear safety goggles and work in a well-ventilated environment with no ambient smoke. Never touch your eyes or mouth after working with Freon or other chemicals. Wear long sleeves and gloves whenever possible. ^{[9] X Research Source}

Steps

Initial information gathering

Diagnosing air flow problems

Diagnosing problems at air temperature

Warning

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