Need refill specs for old 911 factory a/c

jclc · 05-08-2002, 02:29 PM

Hi everybody,

I'm just finishing a major teardown and repaint of my 74 911 coupe, and was wondering if anyone knows the weight of Freon R12 needed, and the amount of compressor oil that this system uses.

It has the big York compressor with both the forward- and engine grille-mounted condensor coils. I'm petty sure that this is the 'factory' system, all components have 911 part numbers and match those in the 911 parts book.

The system was working fine when I took it apart. I have just replaced the dryer with a new one, and changed out all the old braided hoses with new barrier style hoses. There's some oil left in the compressor, but I have a feeling that this should be drained out and replaced.

thanks in advance,

Jeff Craddock
Orange, CA
74 911 Coupe (now in beautiful Speed Yellow)

stormcrow · stormcrow's Garage

you can't just add refrigerant by the lb to get it right. You need to take pressure readings along with air temp readings in the cabin. You can also check the system by checking the superheat which can vary from 12F to 20F - 15F is the norm for some systems.

Pressure is relevant to temperature. You should have a mim temp diff of about 20 degrees between the temp entering the evaporator and the leaving temp of the evaporator.

If the cabin is 70 f then the supply air temp should be 50f. Shouldn't get below 45f, but if you can get it that low without the head pressure going out of sight, then your system is working at max.

Steve

Jim Sims · 05-08-2002, 06:21 PM

Stormcrow is right, you really need a refrigeration harness with gages plus thermometers to fill a system correctly. That being said the installation instructions for a 1973 "factory" A/C kit specify 26 ounces of R12 refrigerant; this is the kit that had the auxilliary condensor mounted in the left rear wheel not in the front. The instructions are from Porsche but the brochure was printed by Volkswagen. Based on the 1973 factory parts catalog and a collection of parts I have that were salvaged from a wrecked 1973 911E there is also a "factory" setup with an auxilliary condenser up front behind the spoiler; I don't have the fill spec's for that system. Both systems used the big "York" compressor. I also have a set of 1976 "factory" A/C kit instructions and it also specifies 26 ounces of R12 (again it has the big York compressor) even though it doesn't have an auxulliary condenser; perhaps the engine hatch mounted condenser used in 1976 is larger or has more tube length/volume. I have them both ('73 and '76); I'll have to compare them. Not exactly what you wanted but a couple of data points netherless. Remember, don't run your system with the hatch open so there's no air flow over the condensor. Cheers, Jim

Early_S_Man · 05-08-2002, 07:27 PM

Per the 'TRA Supplement' section of Volume II of the factory service manual ... the early factory Behr A/C system uses 39 oz. of R-12, or about 2.6 15 oz cans ... or about $90 worth at current Texas rates for R-12!

jclc · 05-08-2002, 07:41 PM

Thanks guys! anybody know how much oil to use?

Early_S_Man · 05-08-2002, 08:05 PM

No quantity of oil is specified, but rather the depth of oil using a dipstick in the inspection port hole (plug on top of compressor body) is specified as 30 mm or 1-3/16" ...

jclc · 05-08-2002, 11:31 PM

Warren,
Dumb question- Does the oil level spec apply before the system is charged (or after its run for a while)? I hear the oil will be distributed throughout the system...
thanks
Jeff