My AC stopped working and I traced the problem to the AC clutch not engaging when I press the AC buton on the dash. I found that if I connect the wire lead from the clutch to the posative jump start terminal the clutch will engage, yet when I reconnect the wire the clutch does not engage. I can hear things happening in the dash when I press the AC button, but it doesn't turn on the compressor for some reason. What could be the cause of my problem? What items could I check, or what could I do to fix it?

Thanks for your help. I would greatly appreciate any suggestions you could offer.

Chris Clarke
85 US 5 speed

 

Most of the time it is the compressor clutch relay which is located in the HVAC console. It's grossly underated (.5 amp comes to mind) and the auxillary contacts burn out. Alot of people are replacing that relay with one readily available at Radio Shack. Try looking on Nichol's Tip site, i think there is a good write-up on the relay replacement.

 

By the way.. you will still hear the relay "clicking" inside the dash even if it's bad because the coil is still working even though the Auxillary contacts are not closing. Someone correct me if I am wrong, but there is also a freeze switch to shut off the comp. if the system temperature gets too cold , and a pressure switch that will prevent the clutch from engaging if there is not enough system pressure.

Ben Burris

86.5 Indischrot AT. #1459

 

I think this is the one being refered to?

 

ALSO - if you have leaked out all/most of your Freon, it will NOT come on. You can test for this by jumping the sensor on the drier/recvr.

 

Hmm.. I have the exact same phenomena...

Dumb question.. Anyone have a pic of that drier/recvr sensor that should be jumped?

 

My first post on this forum Hope it's helpful.
I had the same problem a few weeks ago. Eventually traced it back to the small relay already mentioned earlier. I haven't replaced it yet but managed to prise the plastic cover off and cleaned contacts with a quick rub using 1000 grade wet and dry and a quick spray with electrical contact cleaner. Nice and cool now and has held out for a few weeks but will replace if it goes again.
Shorting out the pressure switch may determine low gas but could also be a dodgy pressure switch. If the comp does fire up by shorting the switch then it's probably wise to not run like that for too long even if cooling takes place as it is there to protect the compressor i.e. low gas can= low oil.
Long term non use of the air con in any car can cause seals to shrink and allow gas to escape but in my experience does not seem to be such a problem on the old R12 systems which use a mineral oil to lubricate.
If you are anywhere near Bedford in the UK I have gauges and can easily determine gas pressure using them.

While I'm here I would like to thank other members of this forum. I have turned my once rough runner into a fine beast using info gleaned mostly from this forum (all the usual vacuum/electrical probs now sorted).
In my early 928 ownership, John Speake diagnosed a prob which would have taken me a long time to find (Hall Sensor) which turned out to be just broken wires (exposed to heat I suspect) replaced wire only (sensor was fine). Just a few minor niggles left now (electric mirrors and interior lights mostly).
Thanks everybody.

 

 

Just spotted you're a US 5 speed so my gauges in the UK aren't much help.
sorry!!
Cheers
Paul
89 S4 Auto

 

Thanks for all the input, I really appreciate your advice. After reading over the replies I think that my problem is a lack of pressure. I put a gage on the high and low side schrader valves and nothing registered. I also tried opening the valves by hand and all I got was a faint hiss that quickly subsided. Now there's nothing at all. Does this indicate that my system is empty? I have a couple of old cans of R12 laying around. Can I simply recharge it, or do I need to add oil or do other things as well?

Thanks again for all of the great information.

Chris Clarke
85 US 5 speed

 

Paul, if you sanded off the extremely thin, hard plated coating on the contacts then they will fail sooner rather than later. YMMV.

 

With the A/C system off the pressure on the low side or receiver/dryer should be close to the ambient temp. Not exact but close...70 F should be close to 70 psi. However while running it should be around 24 to 44 PSI at the receiver dryer.
Carl.

 

FWIW:

I converted my 928 to R134a with one of those 30 dollar kits that includes oil, leak sealant, and the refrigerant a year ago and the A/C is working fine. The system was completely empty... I did NOT change out the drier, empty the compressor oil, or pull vacuum on the system first. A lot of people think I'm an idiot. But it is working, and the system gets a serious workout in the summertime. The kit I used explicitly states it is compatible with remnants of R12 and the R12 oil, so that may be the key to my 'success'.

I've converted several other cars this way (2 Volvos and a 944) and have an aggregate of about 9 troublefree years.

But just to set the record straight: doing it my way is improper and could theoretically cause problems with the compressor. YMMV.

 

Dave,
If Paul took the output wire to the compressor and used it to switch on a conventional 30 amp relay (#85-> #86), this would greatly lessen the current draw across the controller relay. Useing #30 -> #87 of the 30 amp relay to deliver fused power to the compressor is the other half of the equation.
Do you think this could adequately lengthen the life of the puny, sanded contact set within the controller - enough to avoid its replacement?

 

I found a leak in my AC system which I believe is the source of my problems. I attempted to charge my system with R12 and heard a hissing sound. The leak turned out to be from the compressor itself. One of the hose flanges bolted to the compressor body with 2 allen head screws was leaking. Green fluid was seeping out of the joint, which I assume is dye added to the system in the past. Now that I found the leak, I'm not sure how to fix it. Is there a gasket in the joint that I could replace, or is it more complicated than that?

Thanks again for the advice,

Chris Clarke