R-134a Retrofit Bulletin
Before you buy that quickie-retrofit kit, read how Porsche retrofits A/C systems to R134a. The TSB includes all part numbers required for each of the models covered. The TSB is 13 pages long.
It is not that much more work to do your A/C retrofit to factory specifications.
SELECT: Porsche A/C
SELECT: TSB 89501 - Retrofitting R12 A/C System to Refrigerant R134a
84 944 - Dark Gray/Black
80 924Turbo - Silver/Black - my parts car
85 944 - Garnet Red/Black - my other parts car
I just finished reviewing the AC SB concerning the R134a conversion, and was surprised to see that all the seals do not require replacement.
Am I mistaken, or hasn't the general post been to replace all old seals as they are incompatible with the new refrigerant?
A simple drier and fill-valve replacement sounds quite a bit more pleasant than a total seal swap!
86.5 Indischrot 5-speed
After doing the R12 -> R-134a conversion to my '89 S4, I figured it would be a good idea to at least peek at the PCNA tech service bulletin to see if I missed anything. Thanks to F.R. Wilk for pointing the way to that document online. The procedure they propose is somewhat simplistic, and in my opinion incomplete. If you are considering making the move to R-134a from R-12, think about the reason you are changing. It's probably because of a leak in the system someplace, or poor system performance due to leakage sometime in the car's life. Maybe it's because of some catastrophic compressor failure. No matter-- the TSB is targeted at vehicles that are running perfectly on R-12, and only are changing because of the driver's green conscience. Note that the TSB proposes a sweep with R12 to get more old oil out, so it includes the cost of that extra 3lbs of gas, plus an additional recovery cycle. Not a bad idea, just a little expensive compared with manually draining the compressor.
So-- Leak-check the system with a known good electronic gas sniffer before and after your conversion. The o-rings in the couplings and components do tend to leak in their old age, and there are plenty of them especially on M570 optioned cars (rear air conditioner). Fix any leaks that you find, and consider replacing all those o-rings just to be sure. It adds a few hours to the project, but gives you a fresh start with regard to system life.
Replace the expansion valve(s). Using the correct valves lets you get the best evaporator performance with the R-134a gas.
The TSB recommends a Porsche-branded refrigeration oil they describe as ND-Oil 8. My local Nippon-Denso service and supply operation in Long Beach recommends the polyolester refrigerant oil for their equipment in R-134a service. Porsche's only description in the TSB is that their oil is "of a synthetic type." It may be the ester oil in a fancier bottle. There are some watchouts when using the ester oil, specifically with air and moisture exposure during the conversion process. An interesting option for system oil fill is to "vacuum" the oil charge in following the second evacuation, never exposing the oil to more than a few minutes of air during the process.
On the TSB page for my '89 S4, the TSB recommends a straight low pressure adapter, and the angled high pressure adapter. Most charge hose kits now come with right-angle quick-disconnect fittings on the end of the hoses so, at least on this car, it makes sense to use the angle adapter fitting on the low pressure charge port. Their recommendation for not removing the existing schraeder valve core when installing the straight adapter does not apply to the third-party adapters commonly available. Plan on removing the old valves when either adapter will be installed.
I just converted from R12 to R134a last week - I replaced all my o-rings, (except the two at the firewall) and the receiver dryer. I did not replace the expansion valve, although it would be easy to do so.
The Porsche tech bulletin for retrofitting (number 9501) specifies the following parts for 1987-1989:
Receiver Dryer 944.573.943.00
o-ring 7.5x2mm 928.707.247.40 (I actually replaced about 12 of them,
don't remember the exact count. Remember to coat with fresh oil before installing)
High Pressure Valve 928.573.965.03
Low Pressure Valve 928.573.965.00 (I actually used adapters instead of
changing the valves - $12 @ Autozone)
300ml +/- 20ml of Esther oil
2 Labels 964.701.141.02
860g R134a (1030g w/rear air)
The entire procedure took me about 8 hours total, but I took everything off the passenger's side of the engine (compressor, smog pump, brackets..etc.) and cleaned everything while I was in there.. Otherwise
you could probably do the entire thing in about 2-3 hours.
I had my mechanic evacuate the system (before) and then re-fill it when I was done.
So far the A/C works very well and doesn't appear to be leaking anywhere. It held vacuum for 15 minutes before being filled. (After being drawn down for an hour)
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