Why is My Car Air Conditioner Blowing Hot Air?

by | May 15, 2017 | Auto Questions, Car Problems & Repairs

It’s that time of year again. The days are getting hotter. In fact, here in Columbia, MD we are expecting the temperature to hit the 90’s this week.  If your car’s air conditioning system is blowing hot air, don’t sweat it out. Take care of it now.

Car air conditioning systems are complex, and many things can cause the system to fail.  In the illustration below, you can see the some of the parts that make up an automobile’s air conditioning system.

The automotive A/C system includes the control system, sensors, switches and vacuum lines as well as the refrigerant system. A problem with any of these components can cause your car’s air conditioning system to become weak or stop working. These components are tucked under the dash panel and connected through high and low-pressure lines to the engine compartment, the condenser, the compressor, and the drier.

When you come in to get your air conditioning system fixed, the first thing we need to do is diagnose the problem. We give you an information sheet that includes the items covered in this blog post to help explain the process.  If you like, we can even show you the sheet our technicians use in checking and repairing an air conditioning system. Diagnosis can take from one to two hours, depending on the complexity of the problem.

Here are some of the checks that we perform as part of the diagnosis

  1. Road test the vehicle to check the vent temperature and controls including the fan operation, speed, and air flow.
  2. Perform a visual inspection of hoses and lines for leaks. Make sure that the compressor is free of obstructions, and check the condition and operation of the compressor clutch.
  3. Ensure that the condenser and cabin air filter are free of obstructions.
  4. Check the operation of the condenser fan and the air conditioning compressor.
  5. Connect a refrigerant recovery machine to the AC system, and check pressure readings.
  6. Evacuate, recycle and clean/dry the refrigerant. Then fill the refrigerant to the correct level and add dye to assist in checking for leaks.
  7. Perform an electronic and/or black light checks for leaks.

Once all these steps have been completed, we can provide you with a report of any leaks as well as an estimate of the cost to repair the system.

Sometimes air conditioning leaks can be very hard to find because we are looking for an invisible gas. The dye (mentioned in item #6) helps us to locate the leak. Occasionally the holes are so tiny that we have to let the customer drive the car for a few days, and then have them come back to recheck for leaks.

Leaks in the engine compartment are easier to find, but leaks from the evaporator are much more difficult because the evaporator is tucked away behind the dash panel.  In the photos below, we are working on the evaporator core.  As you can see, the dash panel has to be removed to repair the system.

Auto Air Conditioning Evaporator Core Service 1Auto Air Conditioning Evaporator Core Service in Columbia, MD - Removal of dashboard

If the air conditioning system has failed because of an electrical or electronic failure, then we handle it in the same manner as other types of automotive electrical or electronic issues.  This involves performing various tests to pinpoint and then correct the problem.

A common failing of auto air conditioning systems is refrigerant leaking from the service caps that are used to connect the gauges. This is one of the areas that we check for leaks. If you don’t currently have a quick seal service valve cap, a good preventive maintenance measure is to install one.  It can help to protect against these types of leaks.

So…be sure you’re ready for the next heat wave.  We even have a diagnostic form that you can complete and bring in with your car on your service visit. It can help speed the diagnosis process.

Sometimes your car’s air conditioner can be working one day, and not working the next.  We call that an intermittent AC problem, check out this blog article if you think you are experiencing an intermittent AC issue.

Note: This article was originally published in 2014, but has been updated.


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About the Author

About Brian England

Brian England, the current president of BA Auto Care (formerly British American Auto Care), got his start with an auto apprenticeship in a small town in northwest of London. He came to the U.S. in 1972 to work for a Land Rover dealer in Rockville, MD. A few years later, he started British American Auto Care with his wife, Jennifer. Brian is a big believe in preventative maintenance, and his philosophy is to encourage and educate drivers on the benefits of a regular maintenance plan.