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Does the clutch ever engage under control of the HVAC head? You should be able to start the car, turn on the A/C and watch/hear the clutch engage. If that doesn't happen let us know.
If the compressor is running and you aren't getting cold air that suggests you have a coolant leak (actually it suggests you have no coolant). I'd pony up $50 and buy myself a gauge set, another $50 buys you a hobbyist vacuum pump. If the shop put fluorescing oil in during the re-charge you should be able to find leaks with a UV lamp.
See Wally's post 2. I assume he is referring to his guide. [on re-read, it is not Wally's guide] Follow the voltage back from clutch, to low pressure switch, to freeze switch which should have 12v on both wires into it. I'm guessing you don't have any power there, which means the problem is in the control head. Search for threads on HVAC control head.
Also Dwaynes Garage: "http://dwaynesgarage.norcal928.org/1987%20HVAC%20Vacuum%20Leak%20Testing%20and%20Repair%20Procedure.htm" is an excellent write up on HVAC vacuum issues.
When the AC system looses the refrigerant there is a reason for it.
You need to replace all the seals, the expansion valve, the receiver drier, drain and replace the compressor oil with fresh and proper amount.
Then vacuum the system down for a long time (4+ hours with a good pump), and confirm vacuum holds. Then and only then fill the system to the proper level.
I will never "top up" an AC system. It is not worth it.
I do however verify that the relay in the head unit is functioning properly, and what the pressures are prior to starting.
When the AC system looses the refrigerant there is a reason for it.
You need to replace all the seals, the expansion valve, the receiver drier, drain and replace the compressor oil with fresh and proper amount. *pressurize the system with Nitrogen and see if it holds
Then vacuum the system down for a long time (4+ hours with a good pump), and confirm vacuum holds. Then and only then fill the system to the proper level.
I will never "top up" an AC system. It is not worth it.
I do however verify that the relay in the head unit is functioning properly, and what the pressures are prior to starting.
Why spend 4 hours vacuuming it down to only find it won't hold, fix next leak and then spend another 4 hours on vacuum to test.
Fair enough Sean,
I can tell right away if there is a leak or not when I start the pump.
But pull the vacuum down then turn off monitor for a leak, if it holds pull down for a few hours.
Mads - you say this shop is one of the best locally - they sure aren't acting like it...
It seems very very likely you have a leak - unless you want to get a bunch of gear and do it yourself you'd be best to get a pro to do this part.
BUT they actually have to know what they are doing, care to work at it, and be thorough - none of which they have done so far.... You have simply got bad service from them so far.
If they didn't have time to do it right - they shouldn't have touched it at all..
As Colin says its a waste of time just topping up - the fact that you need to tells you that you shouldn't because you must have a leak! they should know they are just wasting your money doing this...
Some shops are intimidated by a Porsche - thinking it has something exotic - we don't - the 928 has a very standard 'vanilla' AC loop - nothing unusual at all. The hardest thing for them is the electrical side - you can help there. As long as the Freeze switch gets power in AC mode and the compressor can turn on with the pressure switch bypassed they should have no issues diagnosing the system.
Evaluate for electrical issues driving the clutch - you should check this yourself using the guides here (Dwayne's etc - lots of posts on the head unit relay all the way to the compressor).
I think i found the problem... The shop i went to last year has put the R12-R134 connectors on the wrong way. So the high/low side is switched over... I hope this did not ruin the system.. I will get a new appointment with the 'new' shop and get the connectors switch over.
Putting the adapters on backwards won't harm the system, but it could easily harm a mechanic working on the system. You can swap them yourself, they just unscrew. I'd say this pretty well verifies the folks you took your car too didn't do a good job; putting the low side coupler on the high side is a bit like leaving a bomb in your car.
PS: I didn't actually check to see if the fittings were backwards, I just took your word for it. It's a very odd thing to do so you should make absolutely certain the adapters have been reversed. If you swap them in error you could seriously hurt/kill yourself or someone else.
08-04-2014, 05:44 PM
