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It’s hot!

Written by Randy Gerdin on July 1, 2017

This year we seemed to go from winter to summer in about 10 days. I heat my house with wood and had the wood furnace on in the morning and the air conditioning on the same evening when we got home from work. Crazy! We have also been seeing a number of vehicles in the shop lately with their air conditioners (AC) not working. AC can be a confusing issue. There are a lot of different configurations on the market. Some vehicles have standard AC, some have dual climate control so that each side of the front seating area can control their own temperature. Some SUV’s, CUV’s, and vans have rear heat and AC. This means that the AC system has to run under or inside the body to a rear evaporator core (the part that gets cold) in the rear for the far back seating positions. The parts under the hood are the same, but they branch off to provide cooling to the rear.

Since about 1992 all vehicles use a refrigerant (known in the trade as “freon”) called R134a. This is the industry standard and is what all the manufactures have used for years. In some very new cars, the manufactures are starting to switch over to another refrigerant that is supposed to be more environmentally friendly. Unless you have a brand new model of a certain make and model, you most likely have R134a. I have read articles about people trying to substitute other chemicals into the system. These alternatives are not approved by the manufacture and can actually harm the system. R134a in an uncompressed state is a gas, or vapor. When compressed or pressurized, it is a liquid with a boiling point of -26.3 degrees C. That is cold. So when our vehicles are just sitting around not being driven, the freon is in a gaseous state. When we start the engine and turn on the AC the magic begins.

Our car systems work basically the same way as our home AC or a refrigerator. The freon is pumped around with a compressor and changes state from a gas to a liquid and back to a gas again and out comes cold air. We in Minnesota have a bit of a unique situation with our AC systems. The AC actually will come on in certain situations when the ambient temp is cold and we have the defrosters on. This helps to keep fog from forming on the inside of the windshield. Also, here in the colder climates, we have the unique problem of our systems retaining their charge. It is not that uncommon on a six to ten-year old vehicle to have to charge it up every year or so. Unless we find a specific leak, the systems over the winter can slowly lose their freon due to the contraction in all the fittings and O-rings that seal up the system. In some cases, freon just seeps out.

In many cases, freon leaks are difficult to locate. The standard practice these days is to evacuate the system and let it sit in a vacuum state and see if the system will retain its vacuum. If it does, then a small amount of ultra-violet dye is added and the system is driven down the road to circulate the Freon. Then a black light is used to look for a leak. We also use an electronic leak detector to help isolate leaks. Very small leaks can be difficult to find. Especially since so much of the system is hidden inside the dash, in front of the radiator, behind the engine, inside the body or inside the rear evaporator case in a rear unit. In many cases if a leak is not initially found, the driver may have to drive for a while and return to the shop for further inspection. In some cases, parts of the vehicle will need to be removed to inspect unseen parts. Sometimes the leak is found other times we just have to keep looking.

One word of caution, NEVER EVER add AC sealer of any kind to the system. It is never recommended and can actually plug up the entire system. We saw it twice last week. The other problem with sealers of any kind is that if a shop is unaware of the chemical in a system and they hook up their AC machine and it contaminates their machine, the AC charging/recovery machine can be damaged beyond repair. These machines are thousands of dollars. Again, please don’t try and cheat the system with a mechanic in a can. It can bite you. I Hate When That Happens!

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