Auto Air Conditioning: Retrofitting

Starting in November of 1987, with the signing of The Montreal Accord, Retrofitting became a popular topic among car enthusiast. With R12 no longer available for the do-it-yourself mechanic, everyone was talking about converting his or her auto air conditioners to the environmentally safe R134a refrigerant. In 1994, auto air conditioners started using R134a as a refrigerant.

Today, as older vehicles are finding their way to the salvage yard, fewer people are talking about retrofitting their auto air conditioners to use the environmentally friendly R134a refrigerants. Retrofitting may still be a viable option for you if you are into restoring older cars like many of my readers are. You can still retrofitting kits for most old cars that contain everything that you will need to make the conversion. You can do the conversion yourself, except for the recovery of the R12 refrigerant, which must be performed by a licensed automotive air conditioning mechanic.

Things That You Will Need

Basic mechanic's hand tools

An air conditioner conversion kit

R134a compatible compressor oil (pag oil)

A new accumulator/dryer or receiver/dryer

A new expansion valve

New orifice tube

Refrigeration vacuum pump

Refrigeration manifold gauge set for use with R134a refrigerant

Electronic leak detector

Duct thermometer

Liquid chemical measuring cup

Loctite

How To Perform A Complete Conversion

1. Perform a pre-conversion visual inspection. Conversion kits are not expensive, but before you rush off to your favorite auto parts store or "Big Box" store to buy one for your car, inspect your system. Visually, inspect the system. Look for abraded lines or wet spots on the lines that might indicate a refrigerant leak. Older, R12 systems used a mineral based compressor oil that left telltale stains at the site of refrigerant leaks. Make a list of any parts that you will need to replace during the conversion that are not part of the conversion kit.
2. Perform a pre-conversion performance check. Check the duct temperatures. Check the compressor for noise. Check the compressor clutch for proper engagement. This is the time to make any necessary repairs to the system.
3. Have the R12 refrigerant recovered from the system by a licensed professional. DO NOT release the R12 into the atmosphere. It’s a violation of the EPA laws and carries a stiff fine. It also damages the earth's Ozone layer.
4. Replace the old Receiver/Dryer or Accumulator/Dryer. These components serve two purposes, first they store excess liquid refrigerants, and second they remove water moisture from the refrigerant. Dryers contain a desiccant that absorbs the moisture that finds its way into the system. Desiccants lose their ability to absorb water with age and need to be replaced. Besides that, most desiccants are not compatible with R134a refrigerants, so you need to replace them with one marked "RH7." These components should be replaced anytime a system is opened up for repairs or modifications. Accumulator/Dryers are used on systems that use Orifice tube to meter the liquid refrigerant into the evaporator. Receiver/Dryers are used on systems that employ an expansion valve to meter the liquid refrigerant into the evaporator coil. Remove the old accumulator/dryer or receiver/dryer. Drain the old compressor oil from them into a measuring cup. Pour an equal amount of pag oil in the new component before installing it.
5. Replace the expansion valve or orifice tube. You can disassemble and clean an Expansion valves, but I suggest replacing the old one during the conversion. Many DIY conversion fail entirely, or perform poorly, because the DIY mechanic takes shortcuts and only replaces the parts that come with the conversion kit. I strongly advise replacing these parts during the conversion. If you do not, you may be changing them soon after the conversion is completed. If that happens, you will not only lose the R134a refrigerant in the system, but all the time you have invested, as well.
6. Perform a complete oil change on the compressor. Unfortunately, there is no convenient oil drain plug on a compressor as there is on your car engine. You will have to remove the compressor to drain the old compressor oil from it. Measure the old oil and replace with an equal amount of pag compressor oil. Changing the compressor oil is only one of the things that are omitted from the instructions that come with a conversion kit. The conversion instruction also omits information on accumulator/dryers, receiver/dryers, and orifice tubes, all serious omissions.
7. Coat the new "O-Rings" with compressor oil when installing the new components. A liberal coating of new compressor oil will help the O-Rings seal properly and it will make them last longer.
8. The hard work is completed. You now install the parts that came with the conversion kit. The kit contains two adapter fittings that convert the high side and the low-side Shrader Valve service fittings to quick-disconnect fittings. Since the new fittings will remain in place, I use Loctite on their threads to ensure they do not work loose from vibration.
9. Hook up your air conditioning manifold gauge set. Connect the "Red" hose to the high-side service fitting. Connect the "Blue" hose to the low-side service fitting. Connect the "Yellow" hose to the vacuum pump.
10. Close the high-side valve on the manifold gauges and open the low-side valve on the manifold gauges.
11. Start the vacuum pump and pull a vacuum for 30 minutes. The "Compound Gauge," the low-side gauge on the manifold gauges, should read 29" of Mercury (Hg.) stop the vacuum pimp and let it set for 30 minutes, check the compound gauge, the reading should have held steady at 29" Hg. If it dropped you, have a leak in the system that you will have to locate and correct.
12. Charge your retrofitted system with R134a refrigerant. When the system is fully charged with R134a, the low-side gauge will read between 25 and 40 psi and the high-side gauge will read between 225 and 250 psi. The ideal low-side pressure is 35 psi but this will vary with the outside temperatures.
13. Perform a performance check by measuring duct temperatures. The system will run one to two degrees warmer than before the conversion, but that is normal and to be expected.

I have seen many professional mechanics skip several of the steps that I have outlined above and the conversion worked fine when they finished. The question is how long they continued to work. Using R134a in a system that still has POE compressor oil in it is a time bomb because POE oil and R134a are not compatible.

Have you read my other articles on auto air conditioning?

Auto Air Conditioning: How to Recharge Your Air Conditioning System

Auto Air Conditioning: How To Find A Refrigerant Leak

Auto Air Conditioning: How to Evacuate the System

Auto Air Conditioning: Why Does It Blow Hot and Cold?