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What to do when your vehicle air conditioning is blowing hot

Updated on May 6, 2013
air conditioning components
air conditioning components | Source

So the country has been experiencing a heat wave and my shop has been flooded with A/C concerns. I figure now is a good time to share some information about properly servicing and diagnosing some common concerns.

A brief lesson on air conditioning. The system's primary purpose is to remove the moisture from the air. Ever notice the puddle of water under your car on really hot, humid days? Dry air is cooler, which is something I think most people know in this kind of weather. Also, the air conditioning system dries the air in the wintertime which helps with defrosting the windows. I get a lot of people that mention that the a/c worked fine before winter, but they didn't run the system during the winter so why would it be acting up? Most are surprised to know that in defrost mode, the a/c automatically kicks on.

The key components of most air conditioning systems are the compressor, condenser, evaporator, drier and expansion valve. Of course, multiple lines tie in all of these parts as well as some sensors. All of these can allow the freon, an odorless and colorless gas, to leak out. In larger SUV's and vans, lines also run to the back to a secondary evaporator. In very general terms, the compressor pumps the gas through the system where it pulls heat and humidity from the inside and passes it out of the car, returning with cool, dry air.

When the system stops blowing warm air, often the first place to check is the amount of freon in the system. If the system is low, it's because it leaked out somewhere. If the system is not low, then there will be an electrical problem. This simple check is a life saver when it comes to diagnosing a problem.

If the system is low on freon, a machine is used to remove the remaining portion. Then a vacuum is placed on the system to see if there are any large leaks. Kind of like if you put your hand on the end of a vacuum sweeper hose. If you open your fingers, the vacuum goes away. So as long as the system holds relatively well, the system gets recharged with freon and a fluorescent leak dye. After the system is ran a while, up to 2 weeks, then a uv light is used to find where the dye is coming out at. This is the most common situation associated with a/c systems.

Depending on what has failed, repair costs can range from about $250.00 to $1200.00. A simple switch can be replaced and the system recharged for about $250.00. An evaporator core, which is in the dash, can be closer to the $1200.00. The labor times vary depending on how complicated a vehicle's dash system is.

All auto parts stores offer do-it-yourself a/c recharge kits which can work well to get you by, but a couple of words of caution: be sure it needs it because overcharging the system can freeze up the compressor and cause new problems! Also, some kits have a 'leak sealer' in them. This sealer can work well at stopping small leaks but can also clog up other parts of the system.

So if your a/c system makes you hot under the collar, remember my advice and have it checked by a professional. If the repairs are too costly, just remember, hot weather isn't around forever!


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