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Mine was already converted... (archive)

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Posted by JamesM on June 05, 2002 at 16:24:34:

In Reply to: Has anybody upgraded the 1988 M5 Air Conditioning posted by Jim E. on June 05, 2002 at 15:41:35:


With the later model systems using the newer refrigerant?

My mechanic (old line BMW service manager) has proposed this a way to get a better cooling system in the car. Wife usually drives the car, and in the summer in Florida, I get nothing but constant complaints about the poor AC. Anybody with information, please pass it along.

R134a is less efficient than R12. "Upgrading" is not exactly the right word. My M5 had a BMW/Behr R134a compressor installed when I bought it, and the conversion cost around $1100. You must change the compressor, flush the mineral oil from the lines, condensor, and evaporator, change the expansion valve to an R134a compatible valve, and change the drier. Technically, you need to change the lines, as R12 lines will allow R134a to permeate the rubber over time. You will need R134a "barrier" hoses.

Anyway, you should have the system checked thoroughly. If the compressor is weak, then consider going to R134a. If the compressor is fine, look for other fixes. The drier must be replaced every few years (3-5 yrs) as preventative maintenance. The condensor (in front of the radiator) must be clean and free of dirt/debris, as airflow over the condensor is what cools the hot side of the AC. Clean it thoroughly with a good detergent and a soft brush. Remove the auxiliary fan and clean behind it. You'd be suprised to see how much dirt, leaves, bugs, and feathers collect behind the fan!

If all of these components are working properly and not leaking, then you should have ice-cold AC. When charging the AC, charge by vent temps. Put a thermometer (you can find these at auto parts stores) into the vent, start and idle the engine. With the car sitting still and the engine at idle, charge the AC SLOWLY until the thermometer reading bottoms out. It should register about 36-40 degrees F. The spec R12 charge is listed in the engine compartment. I believe it's around 2.2 pounds. R134a charges should be about 80% of the R12 charge.

Hopefully I will find that simple blockage in the system and I'll have cold AC again.

Have you considered getting the windows tinted? It really helps in my no-AC M5.

You can find TONS of useful info on AC problems/diagnosis on the ACSource bulletin board.

Alternately, you can buy your wife a daily driver with good AC. American cars typically have great AC. I drove an Olds Alero rental in Boca for 2 weeks. That thing kicked ass (except for the **severe** understeer) for an American car.

JamesM



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