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Kate on Cars June 2012 - Chill out! Car Air-Conditioning Failure Basics


Kate on Cars June 2012

Car Air-Conditioning Failure Basics

by Kate Jonasse

Chill out! Car Air-Conditioning Failure Basics

It’s that time of year. You’re in your car on a super hot day and you turn the a/c on, after it’s probably been dormant all winter long. If it starts blowing cold out of the vents, you breathe a sigh of relief and settle into your seat.

On the other hand, some of you will experience something else. Your vents will not blow cold air, they will blow hot air. Then you’ll roll down your windows and breathe a sigh of resignation. Sorry, the a/c doesn’t work today.

Sometimes air-conditioning systems in cars don’t work because they are low on refrigerant due to a leak. Sometimes one or more of the components in the system has failed, causing lack of the correct pressures needed to make cool air for you. Regardless, your first step is to call your friendly local auto repair shop to schedule and a/c system diagnostic. What could have gone wrong?

Well, I just mentioned leaks. They are one of the most common a/c system faults we see in the shop. Even a tiny leak can cause refrigerant to leak out and prevent the system from keeping you cool. Leaks commonly come from service port valves and missing valve caps, hoses, and bad seals. If your system has a leak in it, the leak needs to be found and repaired before recharging the system.

There are several ways your service technician will look for leaks, and the best results come from using all methods together. These methods include a visual inspection, a refrigerant-detector or “sniffer” inspection, and a vacuum/pressure inspection.

When refrigerant leaks, the refrigerant itself doesn’t leave any visual marks like an engine oil or coolant leak would – it just evaporates. But sometimes compressor oil or service dye leak collect around the are of the leak – so a visual inspection of the system is the first step to finding a leak.

A refrigerant-detector is another method to locate an air-conditioning leak. There needs to be some refrigerant in the system for this method to work. A special hand-held piece of equipment with a nozzle is moved slowly along the entire a/c system – it beeps loudly when it “sniffs” refrigerant. Some leaks only occur when the system is turned off, some only when the system is running, and some only on Tuesdays going over bumps – so this method alone isn’t enough. And some a/c components are behind the dash where it’s difficult to impossible to get the detector.

The vacuum/pressure method is another way to detect leaks. By attempting to place the system in a vacuum (using a special vacuum pump), some leaks can cause a hissing noise. And if the system can’t be brought into a true vacuum then a leak is definitely there. But some leaks can actually be sealed by applying vacuum to the system, so we need to put some pressure in the system, too. This means properly adding refrigerant and going over the system with a fine-toothed comb – visually, auditorily, and with a sniffer.

Finding a/c leaks can truly be an art. Sometimes leaks occur in the weirdest places and can’t be found using only the above methods and one has to get creative.

Now, as I mentioned earlier, leaks are far from the only thing that can cause your air-conditioning to not work. Faulty components, like the compressor, condenser, evaporator, receiver-dryer/accumulator, thermostatic expansion valve/orifice tube, lines and hoses, fans and switches can fail. A compressor can make noise when it fails, but this is not always the case. Most of the other components fail silently and have not exterior visual indication that they have failed. That’s where the technician’s brains really come into play, along with good knowledge of how to use the most up-to-date air-conditioning tools.

So if your a/c didn’t work the first time you turned it on, I’m sorry. Call your shop to schedule an appointment for a diagnostic. Please, do not insist on “topping off the system,” or this may cost you more money in the long run versus diagnosing the problem correctly. Topping off a faulty a/c system may work temporarily, but it does not correct the underlying issue.

Best a/c wishes to you all, and I hope you have a chance to chill out this summer!