lear60man

Tis the time of year......I sent my new baby to get her A/C system recharged and the tech told me that the Freon was fine but the compressor clutch was only running for 3-4 seconds at a time before disengaging. Anything I can troubleshoot before I send her to Porsche?
Thanks,
90 C2 coupe 120K

Youcef

Do a search on this one, there is a bunch of posts about A/C clutch operation.

lear60man

I tried that before posting but no luck. I talked to my friend who is a Porsche tech and he said that it is common for Air conditioning guys who are not familiar with this car to overpressurize the system. I released some pressure from the system and sure enough the clutch now engages properly. Now I will have him take the car to work and recharge the system with the right amount of R12.

DaveK

Out of interest - how long does your clutch engage then? Mine cycles - it's usually only on for 10-20s and then off for 10s or so. I've seen this discussed before and some cycling is normal (to stop things freezing up) but I wonder how frequently other peoples cycle on and off.

Randall G.

I'm not surprised your friend said this. If you pick up a generic charge-it-yourself kit at the local auto parts store, the "green zone" for charge on the low-pressure side gauge starts at 25 psi. Per the Porsche manual, max low-side pressure is about 15 psi at 25C (acceptable pressure varies with temperature). Several guys over on the 993 board over-pressurized their systems, following the generic gauge. Didn't get cool air until they bled off some pressure.

DaveK

OK, so I have a question. When my air con was recharged on Friday (from totally empty) it wasn't done by pressure - it was done by weight - 850g. I checked with my mechanics (they are not the ones who charged it) and they confirmed that this was the correct amount.

When he was checking the system worked after this, I do remember him saying that the high pressure was somewhere around 10 - and that he expected it to be a bit higher.

So - should the air con be recharged by pressure, or by weight? And what are the values that should be used?

springer3

Weight is by far the more accurate method, but the system must be evacuated. My car has a decal indicating the correct R12 charge weight.

Getting the charge correct when "topping up" is complicated, but it can be done. You need the inside wet bulb temperature, outside dry bulb temperature, suction pressure, and discharge pressure. Most places just "shoot the juice" until the compressor suction line gets cold. Truth be known, that gets you pretty close under most operating conditions. With the car in the sun on a hot humid day, that method could result in getting overcharged.

darth

If I remember correctly the sticker on the fan shroud said 32.8 oz of R12 to fill the system. Would four 8 oz cans of R12 be close enough or should I be concerned with the 0.8 of an ounce I'm short? When I convert 850 grams to ounces I get 29.98 oz - about 2.8 ounces less than the 32.8oz sticker? Or should I weigh each can and go by weight?

Thanks in advance
Bill
90C2