s4bill

It worked when I got the car. It stopped working just before the car sat for a few years

89 928 s4

I see a bunch of threads and some suggestion on how to troubleshoot specific sections of the AC. I saw Walley's page on 928 specialists that looks really helpufl.

I thought I saw a thread or document that was straight and simple as to where to start the troubleshooting process. e.g. Turn this button and look for this. The AC equivalent of "check for spark, check for fuel....." you get the point.

fraggle

I'm getting a TON of experience at this on my '87 and live in NoVA and may be able to help. I don't know of a nice checklist doc. I should check in the manuals there's probably something in there, though.

griffiths

Wally has some great stuff and there is this site:
http://www.nichols.nu/cat05.htm

s4bill

All of this data is great however where do I start?

Unless I am missing something, the documents dont give an order where to start if you simply have no AC?

Check this first
check this second

or look for this and if this result check this

I will re-read Wally's paper and see if I am missing something.

SQLGuy

I would start by checking whether, with the system engaged, there is 12V on both sides of the low pressure switch.

If there is 12V on only one side, I'd bring the car to a good A/C shop to be checked for leaks and charged.

If there is low voltage on both sides, I'd jumper 12V (through a 10A fused jumper line) to the side away from the compressor and see if the clutch engages. If the clutch does engage at this point, I'd probably pull the head unit and check whether the original relay is in there, and, if so, replace it.

alabbasi

It worked and then stopped .. what does that mean?

Does the blower engage inside the car at all or is it just blowing hot?
Does the clutch engage on the compressor when you hit the a/c?
Have you checked the fuses?
Have you put gauges on the car to see if there is any refrigerant in the system?

Start with the basic tests (like finding the answer to the questions above) and then post again. We may then be able to point you in the right direction.

s4bill

"I would start by checking whether, with the system engaged, there is 12V on both sides of the low pressure switch."

Where is the low pressure switch?

It worked and then stopped .. what does that mean?

It means that it blew cold air and then stopped blowing cold air. It was a while ago so I dont remember if it was an issue of not as cold or simply no cool or cold air at all.

Does the blower engage inside the car at all or is it just blowing hot?

Yes the blower engages and blows hot air. If I depress the AC button so that it is off and turn the fan on high then depress the AC button to on the AC button does light and it seems that the blower fan runs faster or blows air stronger. Not sure if that is expected behavoir?

Does the clutch engage on the compressor when you hit the a/c?

I had someone turn the AC unit on and off and it didnt appear to engage. I checked with a flash light and didnt see any activiy and I didnt hear anything that sounded like something was engaging. Its at the bottom so it wasnt really clear to see but I assume you would hear it engage?

Have you checked the fuses?

I am going to do that now.

Have you put gauges on the car to see if there is any refrigerant in the system?

I dont have gauges. Is there a sight glass or other way to tell?

Randy V

Start by putting some refrigerant into the system.

Easy.

AO

If you go to 928GT.com - look on the left column for "Wally's World" under 928 Tips and Links. There you will find a step-by-step AC diagnostic guide.

An additional tip...
You can temporarily engage the AC clutch by attaching a battery jump pack to it. There is a single lead coming off the compressor. Hook that up to +. Then attach ground to the body of the compressor. You should hear the electromagnet (clutch) energize. I've successfully done this on my car both with the engine off and while running (be careful about the belt turning).

I would not run it for very long as you don't know if there is refrigerant in the system which also lubricates the entire system. But it is a quick test to see if the clutch works or not. If it works, your problem lies elsewhere.

SQLGuy

Not the best advice... unless you're suggesting he just bring it to an AC shop.

SQLGuy

It's attached to the receiver/drier (at the left end of the evaporator when when looking at the engine).

Randy V

Unless you're advocating from the tree-hugger gallery, it is absolutely the best advice.

Getting the system charged will tell him a lot about what is going on without replacing everything on a witch hunt.

Then he can determine if the system is blowing cold and do leak checks.

Boo hoo about the ozone layer if some freon leaks out.

MainePorsche

I haven't seen any mention in this thread as to whether the system is adequately charged. OP states sitting for a couple of years.
Fill it with 1050 gms and then see what you got.
He could be electrically fine, but without refrigerant or oil, he will have no function. Once he knows he has refrigerant, he can proceed methodically.

Tampa 928s

On the compressor is a brown coated wire that connects from the passenger harness near the cam cover. The connector is long and plastic with a spade connector inside pull it apart. Get an alligator clip touch it to your hot post and listen for a click indicating clutch is working. If it engages turn on your air for only a minute and see if cold air is present. If your getting air your issue is in the clutch controll circuit. If no air get it checked with a set of gauges you have a leak large enough to open the clutch low pressure switch. Do this or waste your time chasing problems. Most a.c. Shops will do this for under 100 paying for your gas as needed and check for leaks. If you have a massive leak then can reclaim the gas and refill it after you corrected your leak.

Randy V

My point exactly.