Re: A/C Compressor & Condenser Replacement
Posted: Mon Jul 12, 2021 8:22 am
Oh --
My target suction pressure is about 20 PSI at the conditions I described above. Your gauge set has equivalent temps for the indicated pressure, and lower/colder is better provided you are still delivering liquid to the expansion valve. Heat from the cabin is boiling the liquid inside the evaporator tubes, and the heat required for evaporation is what "cools the air". My high-side pressures range up to -maybe- 225 on the hottest days, but are determined by compressor and condenser/fan capability, heat load from the cabin including condensing that humidity (as suction pressure), and of course ambient temps.
Note that these are my 928 numbers, but shouldn't differ much in the other cars. For the 928, a clean-sheet project allowed the engineers a chance to include plenty of A/C capacity that the 911 series cars lacked. Folks who have owned air-cooled Porsche cars already know that A/C was an afterthought at best, something no true purist owner would even consider adding. With the US and particularly California markets becoming large fractions of Porsche's world efforts at the time, working A/C systems were a top priority. The head of the 928 engineering and design effort was pilfered from GM, where Frigidaire was already pretty good at maintaining cabin comfort. The 924/944 series had the advantage of all of VW/Audi's accumulated knowledge too as well as their parts bins too. No excuses for suffering in the heat!
My target suction pressure is about 20 PSI at the conditions I described above. Your gauge set has equivalent temps for the indicated pressure, and lower/colder is better provided you are still delivering liquid to the expansion valve. Heat from the cabin is boiling the liquid inside the evaporator tubes, and the heat required for evaporation is what "cools the air". My high-side pressures range up to -maybe- 225 on the hottest days, but are determined by compressor and condenser/fan capability, heat load from the cabin including condensing that humidity (as suction pressure), and of course ambient temps.
Note that these are my 928 numbers, but shouldn't differ much in the other cars. For the 928, a clean-sheet project allowed the engineers a chance to include plenty of A/C capacity that the 911 series cars lacked. Folks who have owned air-cooled Porsche cars already know that A/C was an afterthought at best, something no true purist owner would even consider adding. With the US and particularly California markets becoming large fractions of Porsche's world efforts at the time, working A/C systems were a top priority. The head of the 928 engineering and design effort was pilfered from GM, where Frigidaire was already pretty good at maintaining cabin comfort. The 924/944 series had the advantage of all of VW/Audi's accumulated knowledge too as well as their parts bins too. No excuses for suffering in the heat!
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