AC Intermittent

Well guys, its summer and of course the AC has started to act up. It seems like the clutch will not engage when commanded. Sometimes it does for a while and then it goes back to not blowing cold air. I wait a while an re-engage, sometimes it does and sometimes it doesn't. But when it does the AC seems to be working normally. Any ideas for troubleshooting? Is it the AC clutch or is there a relay, ground wire or something that needs to be checked? Thanks,

If the clutch is engaging sometimes and not others and the air is cold like it should be when it is engaged, its probably going out and you have excessive wear on the clutch plate. I've had success putting shims in there to "push it out" on several other European cars but not on a Porsche but you can try it. Eventually you'll need to get the clutch rebuilt/replaced or just replace the whole A/C compressor with one that includes a new clutch assembly. Check out this site and it will give you an idea on what I am talking about : http://www.matthewsvolvosite.com/ac-clutch-shim.html Its also possible you have an intermittent A/C relay - find and test it if the above doesn't work.

There is a relay in Relay Support 2 - underneath the carpet behind the seats Also check the wiring harness to the AC comp. I remember one guy found the wiring harness connection was loose causing intermittent problems. There are also high pressure/low pressure cut off switches, so you might go to an AC shop and check the charge on the system.

The AC will cycle on and off more rapidly when the refrigerant charge is low. If you let it get so low that it refuses to kick back on, recharging the system becomes much more challenging.

Have you put a gauge on the system to check the pressures. There is a pressure switch that prevents the compressor from engaging it the pressure is too low. This should be the first step. If the system needs charging have it charged and see it that clears up the problem. These cars are pretty old, and while it should not leak down much it is fairly common. You can swap out the relay to see if it is bad. Not sure how to test the pressure switch, but to replace it you must discharge the system. My AC quit last year and I finally got around to fixing it this year. Gauges should that the high and low pressure sides were the same so the compressor was not engaged. The clutch was spinning though. A mechanic friend that works on our company truck but won't touch a Porsche, suggested that I first try replacing the expansion valve. This id not work. The cost of buying just the clutch was $835.44 from Porsche and I could not find just the clutch from anywhere else. Porsche lists the compressor and clutch for $1,627.68. It is a Denso unit and you can find them all over for much less. I bought one from Rock Auto for $278 and it is the exact same compressor that came out of my car. I also bought a new expansion valve, a dryer and a set of O'Rings. The total for all of them was less than $350 shipped. When I took the compressor off I could see that the clutch was totally burnt out, so while it spun it was not spinning the compressor. I also bought a set of gauges ($59) and vacuum pump ($99) from Harbor freight. R134A you can buy at any auto parts store for about $12/can. I evacuated the the system, replaced the compressor, expansion valve and dryer, evacuated the system and charged it and it worked great. However, after a week or so it lost some of the charge. I put in some R134A with dye, bought a UV light and glasses for about $25 and found the leak was at one of the fitting attached to the new compressor. This was the one connection that I had to get the o'ring at the dealer at the generic set of rings I bought is not have this one. I just reset the fitting, evacuated the system and charged it. It blows in the low 30's and have held the charge for several weeks. So all the parts came to a little over $500 and I spent several hours in my time. I am sure the dealer would have been $2,000-$3,000.

I bought a can of 134 and it came with a gauge. I hooked the gauge up and it red full right, in the red, in the 150's. I had the ac on but I couldn't see the clutch spinning.

Quotes source post: 13499838

Do not hook up the can if the compressor is not running!! The can could burst due to excessive pressure.

Did you check the fuse and replace the relay? Did you check the wiring harness? Again, I would recommend an AC shop that can check it out and make some recommendations. Maybe a nearby Porsche dealer will help you out for a little $. And like said, if you hook that can up wrong or the compressor is not running it can burst and that will make for a very bad day. You could jumper the wiring harness to the AC compressor from the engine bay 12V jumper point just to see if the clutch is engaging. Recommend doing that while the engine is NOT running. Just a quick test to see if the electromagnetic clutch engages.

Yeah, I hooked the gauge up without the can attached. Thanks for all the input, I'll have a look this weekend.

As Ahsai said, once the pressure is so low that the compressor will not engage, DIY recharge isn't an option any longer.

To test for voltage at the clutch, can I just turn ignition on or does engine have to be running?

I think the engine has to be running and the a/c has to be turned ON at the climate control unit, where everything is being controlled. If you have Durametric, it can activate the a/c compressor clutch even with the engine not running.