Car AC Works Sometimes? Blowing cold today but warm tomorrow?

by | Jul 7, 2014 | Auto Questions, Car Problems & Repairs

One of the most difficult automotive air conditioning problems to diagnose is an intermittent A/C problem.  In other words, one day your car’s A/C is blowing cold air, the next day it’s warm air.

Feeling a bit frustrated?  We know the feeling.


car ac cold one day hot the next

Ironically, the very thing that makes an air conditioning system convenient, easy to use and reliable is the thing that most often causes intermittent problems — electronics.

Over the last ten years more and more features have been added that make automotive air conditioning and heating systems more complex. The first thing to do if you experience an intermittent auto air conditioning problem is to take notes. Record everything related to the event.

1. How long were you driving before the system failed?
2. Were all the air vents starting to get warm?
3. Is the air conditioning control panel functioning normally?
4. How often does the system fail? Completely or partially?
5. Does it fail on the highway or in stop-and-go traffic?

The list goes on and on. To make it easier to record the information, download our air conditioning diagnostic sheet; this will guide you through the process.

The next step is to bring your car in, along with the diagnostic sheet, and have it checked out.

First of all, the basics have to be right. This means ensuring that that the refrigerant system is fully charged, there are no leaks, and that the pressure readings are within the specifications.  Next the electronics are checked for fault codes and any other saved data. Expect to pay from $120 to $250 for this service.

If there are leaks, they should be repaired first, as they could contribute to the problem. Once the system is running correctly and the technician has all the data, the next step is to see if there are any common problems that match the data you have provided and the technician has collected. To do this we use a data base and a hotline. If this doesn’t uncover the problem the technician will hook up monitoring equipment and see if he can reproduce the problem. If the problem still does not surface we might recommend that you drive the vehicle and see if the problem shows up as well as to identify if any of the symptoms have changed. Intermittent problems can be a challenge for both the automotive technician and the customer.  Both parties have to work in partnership to arrive at the solution to the problem.

Common electronic problems relate to sensors that give input to the heating and air conditioning computer and the electronic control head.

People often ask whether it’s worth it to check online to find a solution.  If you are good at performing your own repairs then it may be worth trying some inexpensive suggestions. But if the problem isn’t properly diagnosed, you may end up repairing something that wasn’t actually causing the problem.

For more information about auto A/C issues, check out our earlier blog post.

And in the meantime…..stay cool!


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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.