A/C Not Working? Here’s Where To Start

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Its 90 degrees outside and you get in your car and turn the air conditioner on and only warm air blows out of the vents. You’ve got issues, but don’t fret. There are a few basic things to check first.

The (Very) Basics of Air Conditioning Systems

A compressor takes cool low pressure gas (R12, R134A, R1234yf) and compresses it into a high pressure high temperature gas. This gas passes through the air conditioner condenser (mounted in front of the radiator) and turns into a high pressure liquid.

The high pressure liquid flows through an expansion valve or orifice tube and turns into a low pressure liquid which makes its way into  the evaporator, eventually turning into a low pressure gas.

When the refrigerant passes through the evaporator it absorbs/removes heat. As the cabin fan blows across evaporator the end result is cool air in the cabin.   Then that low pressure gas is again compressed by the compressor and the cycle start over again.

Confused yet? Read Rob Siegel’s book Just Needs a Recharge for a deeper explanation

There are several reason why your car’s A/C system might not be working.

The first place to start is with the basics. In nearly every case, air conditioners use a belt driven pump or compressor. If the belt has failed and come off the compressor – it won’t be compressing the gas. If the belt has failed it could be due to old age, a faulty belt tensioner or a compressor that has seized up.

The next question to ask is: When the air conditioner is turned on, does the compressor engage? If the air conditioner compressor clutch doesn’t engage the issue could be electrical, mechanical or the system is low on refrigerant.

Years back we thought nothing of just topping off an air conditioner system with a slight leak. Over the years two things have happened we have learned that leaking refrigerant, especially R12 (chlorofluorocarbons CFCs) damages the ozone layer of the atmosphere. In addition refrigerant has become quite expensive. So it makes both environmental and financial sense to find and repair a leak.

Some leaks can be detected by a simple visual inspection—sometimes you will see oil accumulated around an air condition hose, at the condenser or at the compressor. This oil is what lubricates the compressor.

You can also add refrigerant that has a dye built into it, the dye is more easily visible than the compressor oil, but indicates the same style leak.  If the system is low on refrigerant and there are no visible leaks the actual leak may be the car’s evaporator.

The evaporator in many cars is buried in the dash and could take many hours to remove and install a replacement. Add in the air bag systems, and this is generally not a job for the DIY’er

If the compressor is turning and the one hose of the air conditioner is warm/hot and the other hose is cold then the problem may be as simple as the fan may not be working. If the fan is not working the fan itself could be faulty, the wiring/switch could be damaged or a fuse is blown.

If the fan is working but the air coming out of the ducts is still warm then the issue could be inside the air ducts. Inside the air ducts, there is at least one blend door that opens and closes to mix air temperature. If the blend door motor is faulty the door will only supply warm air to the cars interior.

If the engine cooling fan or separate A/C fan is not working at the condenser it will also limit air conditioner performance, especially in traffic where air flow is limited.

Although you may get away with adding refrigerant to a leaky system, the system should be checked, the existing refrigerant removed/recycled and the system checked for leaks. During this process the system has a vacuum pump applied which removes contaminants and moisture.    Then once the system is deemed to be in good working order the proper amount of the correct type of refrigerant is added to the system. Adding too much or too little will keep an air conditioner from operating properly.

Like most every car today, even the climate control system can generate computer fault codes. A professional technician will use a scan tool to check for proper system operation.

Any repairs to the air conditioner system should be performed with safety as a priority. Even the DIY’er kits can get you in trouble if you don’t read the directions.