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Per the TSB below, Up to June 1988 for S4s with R12 the capacity with rear air is 1200 grams, or 42.3 oz and without rear air it was 37oz or 1050 grams. Starting July '88 (89 MY) WITHOUT rear air was 950 grams or 33 oz but there is no spec for cars with rear air. By '91 I know it was 1150 grams (40.5 oz) but I dunno if that was true in '89 as well.
Can anyone with an '89 with rear air and the original refrigerant sticker on the radiator report if theirs says 40.5 or 42.3 oz?
I would stick with 42.3 oz. Some is bound to leak out over time by design and I would rather have those 2.7 extra ounces of refrigerant in the system than not.
I just don't understand why the spec changed with the '89 MY, it doesn't make any sense- The 5-speed condenser is the same from -87-91, the front evaporator is the same from 86.5 through early '93, the rear evaporator is the same from 85 through early '93, and the compressor is the same 87-89.
So the only thing that changed in the R12 era of the S4 cars is the compressor, but not until 1990. So why the freon charge change?
My 89 owners manual says 33.5Oz (950g) R12, or 40.5oz 1150g R12 with "additional vaporizer" on page 114 under Filling Capacities.
Pic below.. manual's part no. is WKD 928 021 89 dated 7/88
I assume the fluid capacity of the manual condenser is the same as the auto one? I wonder what the 928 SE owners manual says? They had the 10PA20C in 1988 model year - as its lighter weight.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
It doesn't matter how much Freon you put in the system.
As soon as you turn on the rear A/C the front vent temperature will go up by 10 degrees.
Germans not so good at A/C, back then.
Back then A/C was the only thing Americans had down. The old sealed units from the 70's would be the last thing to die on the cars and many would still work even in junk yards.
Porsche did the best they could, but they just didn't have the condenser capacity to handle all of the evaporator volume.
Back then A/C was the only thing Americans had down. The old sealed units from the 70's would be the last thing to die on the cars and many would still work even in junk yards.
Porsche did the best they could, but they just didn't have the condenser capacity to handle all of the evaporator volume.
Yeah, super tough stuff, that entire needing a solid column of liquid at the expansion valves, which must flash to a gas in the evaporator.
Need a team with doctorates in thermo dynamics to figure that one out.
06-22-2018, 01:21 AM
1989s with rear air: 42.3 oz or 40.5 oz?
I wonder what the 928 SE owners manual says? They had the 10PA20C in 1988 model year - as its lighter weight.
. Thanks Hilton!
