Darien

Ok, my 88 has had an intermitent AC problem since I got her. The PO had it checked out prior to me buying and he was told that the control head was suspect. Up until today I was able to get it to blow cold by moving the temp selector from hot back to cold.

Here's what I know:

The compressor clutch does not engage when turned on
The AC switch is working
The Cooling Fans come on with AC switch engaged
The warm air valve is working

Any other quick check items??

dr bob

Darien--

The Most Likely Suspect is that the car is low on freon. There's a safety switch on the plumbing next to the drier. It has a plug-in with a couple wires attached, and it's not the obvious piece there on top with two screw terminals. Jumper the two wires in the plug and see if the compressor runs. If it does, you have lost enough freon that you probably want to fix the leaks and recharge. Don't try to drive it with the jumper in there. as it will damage the compressor pretty quickly.

If jumpering the switch doesn't do it, it may be the control head relay.

Look at the little AC button, and see if it lights when you push it. The little connector on the back of mine came loose after I worked on the radio, and the AC didn't come on. I reseated the connector (no retainer...) and it worked again.


I'm in Hobbs, working 40hrs days. Close but unavailable right now. ;(


Let us know what you find as far as symptoms.

Darien

I'll check the safety switch next As for the "AC button", I too have fallen on my sword after some radio maint on the 86.5...FYI, the light comes on and the cooling fans also come on when depressed.

I just happen to have some r12 handy in case it needs a top off...thanks

Darien

Well, I jumpered the safety switch wires and still no go. I can here a sound almost like a drag when I jumper them but the compressor does not engage.

As for the control head, when I change the temp from cold to hot and back, I can here flaps moving. Is there still a chance that it could be bad?

I looked and I can't find a good write-up on how to remove the control head...help

Bill Ball

You may want to apply 12V directly to the wire leading to the compressor clutch and see if it engages. The fact that you heard something when you jumpered the low pressure switch leads me to think you need to test compressor clutch directly. If it works, then work backward to the headunit, jumpering the freeze switch harness leads. If nothing happens with that jumpered, then suspect the headunit. It could be the relay. Also, I am not sure from your description as to whether the temp sensor system has a defective inner or outer temp sensor or it is something else wrong in the headunit.

Darien

Thanks Bill...I just found the receipt from when the PO took it in. It states that they traced the problem to the control head. Seems they removed it and cleaned up contacts and touched up solder joints. Also recommends replacing the control head.

After reading other posts it seems that the relay was the culprit most of the time and I was almost out the door to radio shack for the 275-218 relay, but now I'm not sure if I should look for another unit??

j.kenzie@sbcglobal.net

The relay may very well be the only bad part of the head unit. If you jump 12 volts to the compressor wire in front of the passenger side TB cover and the clutch engages, then you have narrowed it down. There are several nice write-up on changing the relay. Hopefully the rest of your head unit is OK. Good luck

Darien

First of all, thanks go out to Dr Bob, Bill Ball for the words of wizdom and Brian for posting the following thread https://rennlist.com/forums/showthre...light=AC+relay

I decided to go for it and replaced the HVAC control head relay with the Radio Shack 275-218 relay. Following the pin pattern as illustrated on Bill's site http://billsworkshop.com/P928S4/xpics/AC%20Relay.jpg , I soldered it together and reinstalled the controller. The AC compressor came to life as advertised when engaging the AC switch and blows cold

Bill Ball

Good job! I told Darien about my first experience with this relay. When my AC stopped working a while back I was so sure it had to be the infamous relay I just went ahead and pulled the headunit and replaced it. The AC still didn't work. That's when I discovered I was just low on Freon.

M. Requin

This tip is great - just did this on mine as a WYAIT while refurbishing my dash. I went ahead and made a wire harness long enough to reach to the CEP since I thought it was getting pretty crowded under the console. Also used the Radio Shack socket for the relay rather than hardwiring it. No real reason to do so, just a why not...

Bill Ball

I didn't know there was a socket for this relay. That simplifies the job. Thanks.

Alan

If you are going to locate it that far away I'd install it on the CE panel - there is always at least one spare socket you can use. This is what Porsche should have done anyway.

If you have a working head unit the best PM is to add an additional SPST relay in series with tthe mini-relay in the stock head unit to drive the clutch load. The wiring already runs through the CE panel so its not hard. You need to get the correct terminals for the relay sockets which is the hardest part. That way its a better relay and easily replaceable & with less load the mini-relay is much more reliable.

Alan

Darien

Forgot to mention that it was the best $8.49 I've ever spent on a Shark!

Since it was my first time it still only took approx 1 hr to complete

M. Requin

I'm back in working on the system (one problem after another to correct, latest is anti-freeze switch) and saw this. I looked for ways to mount the RS relay on the CE in a nice neat way, but your solution is better. Wish I had thought of it at the time or seen your post in time! And I totally agree, this is what should have been done from the git-go by Porsche.