June 25, 2003

Air conditioning repairs
by Jim Kerr

Warm weather has returned and vehicle air conditioning systems are being put to work again. Hopefully, yours is still performing well, but many systems will need some service. Refrigerants have to be the number one area of concern in any AC repair.

Life used to be so simple when all vehicle AC systems used R12 as a refrigerant, but environmental concerns have changed all that. Since the mid 1990's, automobile manufacturers started installing R134a at the factory and still specify R134a as the refrigerant to use in retrofits from R12. To add to the confusion, R22, an industrial refrigerant, has been installed in vehicles by repair shops looking to cut costs, and there are several hydrocarbon based refrigerants (mostly propane and butane) being aggressively marketed by the aftermarket. To prevent problems in the future, you want only pure R134a installed in your vehicle, but how can you be sure?

Have your vehicle's AC system serviced only at a shop that uses a refrigerant identifier every time AC equipment is connected to a vehicle or tank of refrigerant. The identifier will display the contents sampled as a percentage of R134a, R12, or Hydrocarbons (HC) Most units also test for R22, while some units will display the percentage of air in the system. If the system tests 99% pure R134a or R12 (most displays don't show 100%), then it is fine to go ahead, connect the appropriate equipment, and recover the system. Problems occur when another refrigerant or an unknown mix is indicated.

Hydrocarbon based refrigerants can be dangerous. Propane is heavier than air and butane can accumulate in enclosed places. Imagine the combination of an evaporator leak and an under dash spark. Explosions have occurred! Mixed or unknown refrigerants with R12, R134a, and R22 as part of the mix cause a real concern. The Federal Air Conditioning Code of Practice prevents releasing these to the atmosphere, and laws back this up in many provinces. Disposing of contaminated refrigerants can cost higher than the moon and you don't want to be paying that bill!

Some shops will even refuse to work on a customer's A/C system if it has contaminated refrigerant because disposal costs are high and they can't afford to cross-contaminate other customer's vehicles.

Air is another problem in AC systems. Air expands at a greater rate than refrigerant when it is heated during system operation. Too much air in the AC system and operating pressures start to skyrocket. System performance degrades and the high-pressure limit switch may stop the compressor from running. In the old days before recovery stations, systems were always filled with new refrigerant. Air wasn't a problem.

Now air can be introduced with recycled refrigerant, and it can be a significant cause of complaints. Purging air from refrigerant can be done at the repair shop using a manual method to measure the temperature and pressure of a refrigerant storage tank and releasing air until the pressure is correct, or it can be done automatically by the recycling equipment.

If you have an older vehicle that needs AC recharging, a retrofit may be the answer. The availability of R12 is limited, and if you can find it, the costs are through the roof. So why not convert? It can be easy, low cost, and accomplished in little more time than it would normally take to recover and recharge a normal sealed system.

There are three types of retrofits: dirty, clean, and complete. None have anything to do with the appearance of the engine compartment. Dirty retrofits are a simple matter of recovering the old R12, pulling the system down to a vacuum state three times, adding the proper oil, and installing new R134a refrigerant. A different pressure cycling switch may also be required.

Clean retrofits are similar to dirty ones, but include the changing of the accumulator or receiver/drier. New style desiccants in these components are better at trapping moisture that can cause problems with system operation.

Complete retrofits are very rare. They are done following the vehicle manufacturer's recommendations to bring the AC system performance up to original specifications. A complete retrofit may be include a compressor change, or could involve changing every part of the AC system. Unless the vehicle is very expensive or rare in nature, the costs of a complete retrofit are likely not worth it.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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