1973.5 911 Air conditioner questions

ljowdy · 04-02-2007, 01:14 PM

I've done several searches on this and other boards and so far, no luck.

Can anyone with experience tell me about upgrading a stock 1973.5 911T Air Conditioning unit. I've been told that the condenser won't stand the increased head pressure of a converted R-134 freon compressor nor a compressor originally set up for R-134.

At approx. $55.00 per pound for R-12, it seems logical to upgrade and make the system compatible with the cheaper R1-34.

It also makes sense to update the compressor from the standard York model to a rotary that works better more efficient and uses less engine power.

If anyone had done any of these modifications please let me know what compressor you used, what condenser, R-12 or R-134 and if you updated your compressor to a rotary, did you have to fabricate a new compressor stand.

Any information will be greatly appreciated.

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B Goode · 04-02-2007, 01:59 PM

I ran R-134a in my '73.5 for about 6 months. One of the main hoses broke at the metal fitting (my fault for running with a short hose), and I never fixed it.

I tried 134a per the advice of my old neighbor who had worked on many AC systems. He assured me that 134a attacks the O-ring seals of many R-12 systems, but since all of the fittings in my system are metal-to-metal we gave it a shot. I think there may be a couple of nylon-type seals at the compressor itself, but I never had any issues there. My neighbor felt that those York compressors are essentially bullit-proof as long as they are will oiled. Speaking of which, I think that we completely drained the existing oil, and changed the oil type as well.

The AC did blow fairly cold, but seemed underpowered for hot days. My condenser is under the front bumper, which I think may be less effective than other systems. My plan is to eventually go back with 134a once I get the car back on the road, because at this point I wont be out any more than the price of the freon.

Hopefully someone will chime in here with a more scientific endorsement for running R-134a, but I can attest to the fact that it can be done.

ljowdy · 04-02-2007, 02:03 PM

Thanks for that info.... Please keep the information coming

Jim Sims · 04-02-2007, 05:42 PM

911 AC report from Davis, CA

Pressures are slightly higher with R134a but easily within the design reserve of a R-12 system. Leaking hoses will leak more with R-134a. R-12 mineral oil must be changed out (conversions are best done using ester oil or one of the new universal oils) and a new receiver/drier installed. The seals in most R12 compressors will work with R134a and ester oil. You can do much better than the existing unit - 2 cylinder crankshaft type York? A swash plate Sanden is a common upgrade.

ljowdy · 04-02-2007, 05:55 PM

Can you explain "swash plate Sanden"?

thanks in advance

Jim Sims · 04-02-2007, 06:27 PM

I stand corrected; a common 911 upgrade is a "wobble-plate" Sanden compressor.

http://www.sanden-europe.fr/ENG/TypeCompressors.htm

Sunroof · 04-03-2007, 04:47 AM

I have a 73.5T with factory AC. Last year I had to replace all my hoses (took the originals to an AC shop and they used the old fittings as templates and new barrier hoses for a perfect match), replaced the drier, replaced that funky fan switch (asbestos pad backing) on the knee level unit, cleaned the evaporator area (mildew smell from slow condensation discharge), switched out the older fused relay with an updated unit and recharged with 134R. Oh, the compressor was replaced about five years ago with an updated unit. No hoses blew, no issues and 134R works just fine. In fact the system blows cold and holds pressure. No leaks!! I do have the front and rear condensers, but do not use the front blower fan over the front condenser. I disconnected it......

Once you get into the system you find that its pretty ancient! The most interesting find was that fan switch that gets so hot, Porsche engineers applied asbestos backing pads to avoid damage to the switch housing. The switch itself is not expensive and I recommend you replace it as it does seem to give the fan a little more kick. Look in the smugglers box in the trunk on the passenger side and you will see the fused (single fuse) system that should be replaced with the stronger and more reliable updated fuse/relay. Again more cheap insurance and upgrqade.
Replacing and reconnecting all barrier hoses is not that expensive but must be aperfect match relative to the way the fittings are configured. DO NOT throw the old hoses away...The most diificult hose is the one coming off the drier and twisting and turning into the trunk and evaporator. I go over all connections once a year to snug them up and keep the system from leaking.

I went through the, "gotta have R12" mental exercise for months concerned over 134R, before I just did it!!!! Believe me if your system has not been restored, then last worry is what coolant to use.

Bob
73.5T