Air Conditioning Not Working in Your Car? Learn 3 Common AC Problems

Having your car’s air conditioning go out suddenly can ruin your day fast. The most common causes of broken air conditioning are leaks or compressor issues. If your air is blowing cool but not cold, the problem could be a clogged filter, cooling fan problem, radiator trouble, or it could simply be that you need to recharge your AC.

You don’t need to tolerate a stuffy, uncomfortable car, and you don’t need to rely on the shop to fix the problem either. The hardest part of figuring out the right fix is knowing where to start. Check out this guide with three things to check before going to the mechanic so you can diagnose your specific climate control problem. You can save yourself some cold cash by learning how to fix your car’s AC.

How to Diagnose Your Car’s AC Problems

1. Is Your AC Cool but Not Cold?

If the air conditioning is set to max cool and fans on high, but is only blowing moderately cool air:
Check to see that the cooling fans on the condenser or radiator are running when the air –conditioning is on.
Look for any restrictions like leaves, bugs or dirt that would keep air from passing over the condenser.
Check the cabin air filter to ensure that it is not clogged.
Beyond this, the next step is to always check the pressures in the system using a manifold gauge set. The recommended high-side and low-side pressures can be found in your vehicle’s repair manual, or online. Once you have your gauges hooked up, move on to observing the AC compressor itself.

2. Start with the AC Compressor

When diagnosing an air conditioning issue, it’s easiest to begin at the compressor:
With the engine running turn the A/C on max cool, set fans high, and make sure that the clutch is engaging on the compressor. Note: this is not the pulley, but the center piece that engages the pulley to the compressor shaft. If the clutch is engaging and disengaging once every few seconds, this is a sign of low refrigerant. You will also see the low-side pressure on your gauge drop rapidly when the clutch engages, hit a point of too-low pressure, then disengage and the pressure will rise. As you add more refrigerant, the gauge will hold steady, with the compressor running, and should hold at the recommended pressure.

  • If the clutch is not engaging and the system has refrigerant, use a voltmeter to check for voltage getting to the compressor.
  • If there is voltage – the clutch may be bad.
  • If there is no voltage – a cycling switch may be bad, a fuse may be blown, and the system may not have enough refrigerant pressure to trip the low pressure cutoff switch that cycles the compressor.

3. Most Problems are Caused by Leaks

Leaks are the most common problem associated with the air conditioning system. If pressure is low, then there may be a leak:

  • Using a UV A/C leak detection kit is the easiest way to find a leak. Follow the instructions on the packaging to introduce UV dye to the system and UV light to find the leak.
  • Check around all fittings to verify that they are all secure.
  • Check hose manifolds on the compressor.
  • Check the front seal and the o-rings sealing the pressure switches on the back of some compressors.
  • Check where the hoses are crimped onto the fittings.
  • Check the Schrader Valves.Check for pin holes in the condenser.

Check where the evaporator drains condensation with UV light. Sometimes oil or dye can be seen.
Note: The dye check will not work if the system is too low and the compressor is not cycling.

Still Not Sure? Check These Components

AC Compressor and Clutch

The AC compressor is a rotating pump that circulates refrigerant (Freon) throughout the system.

Common Problems: Leaks in one or more seals or the compressor itself can occur. Particle contamination from worn parts inside the compressor are a frequent culprit. The engagement clutch, called an AC clutch, can also fail rendering the compressor inoperative.

What to Look For: If the refrigerant is low, check for visible system leaks that appear green and oily. Failing internal components caused by normal wear or low AC Oil levels caused by leaks. Failed AC clutch. Failed power supply to the AC clutch caused by a blown fuse, bad pressure control switch, dash control module or a broken circuit wire. Inspect and test before replacing!

AC Accumulator / Drier

The Accumulator/Drier collects and absorbs moisture. Moisture is like poison to the internal system components and can damage the AC Compressor as well. Depending on your vehicle, you may have an accumulator or a receiver/drier.

Common Problems: Internal failure allowing desiccant material to enter the AC system. Like sugar in the gas tank, this stuff in the wrong places can cause major problems. Leaks can result in over-saturation of the desiccant material that can lead to compressor damage.

AC Orifice Tube / Expansion Valve

The AC orifice tube / expansion device filters and regulates the flow of refrigerant through your air conditioning system. Depending on your vehicle, you may have an orifice tube or an expansion valve.

Common Problems: Contamination is the main cause of failure. If the system pressures are too high and/or too low, the expansion device could possibly be the issue. But first, ensure the refrigerant levels are correct and the radiator/A/C Condenser fan(s) are working properly. Remember, inspect and test before replacing!

AC Condenser

The AC condenser looks similar to a radiator and works in conjunction with the radiator fan(s). Air flowing across the AC condenser tubes cool the hot (gaseous) refrigerant that absorbed heat from inside the vehicle. This returns the refrigerant back to a liquid state where it will once again enter the evaporator core and absorb more heat from the interior.

Common Problems: Refrigerant leaks. Contaminant particles from the AC Compressor or AC Accumulator/Drier restricting the flow of refrigerant can lead to poor cooling. While checking the AC Condenser, inspect the Radiator / AC cooling fan motor(s).

AC Evaporator Core

The AC evaporator acts like a huge ice cube with holes in it. It allows the hot, cabin air to flow through the core, rapidly cools this air, and blows it out into the cabin again. The cool air felt from the dash vents is provided by the AC heater blower motor assembly.

Common Problems: The number one cause of failure is a leak due to age and wear. An electronic leak detector is the best way to check for leaks. Give attention to the AC evaporator box water drain tube. Use the tester to search for a leak. A green and oily substance may appear in the drain tube if larger leaks are present.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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