90 20V Quattro 1989 model Aircon

Kent McLean kentmclean at comcast.net
Mon Feb 25 03:49:27 PST 2008

whitehill wrote:
> Hi helpful crew.
> I aircond has stop working.
> I have diagnosed this far
> Push the aircond button and the magnetic clutch does not pull in although I can hear a relay somewhere under the dash pulling in.
> I pulled of the wire to the magnetic clutch and put 12 volts on it and it pulls in but and seems to run OK when I start the car but it will not cool - perhaps that it needs re-gassing.
> Is there a sensor somewhere that detects low pressure in the compressor? 

G'day, mate. I'm not going to be much help, but some help is better than none.
You diagnosis sounds reasonable. The AC tries to run, but then some sensor shuts 
it down.

I don't know about a low pressure sensor; there may be. Here's a link that may 
help you find one on your Audi:

I do know there is a low temperature sensor; they AC won't come on if the 
outside temperature drops below (or near) freezing. Although you are still in 
your summer, if that sensor fails, it might be shutting off your AC.

As for the gas -- unless it has  been converted, it is probably R-12, which 
studies have shown to be harmful to the ozone layer. It can be replaced with 
R-134a (HFC-134a), but requires modification to the valves used to fill the 
system. No big deal, adapter kits are available. My Google searches suggest you 
don't need to replace the much else. If Oz is like the States, you may not be 
able to get  R-12 (or it may be too expensive).

You may find more here:


Kent McLean
'99 A4 Avant, w/ quattro, V6, Tiptronic. "Yeah, Baby!"
'94 100 S Avant, "Moody"
'91 200 TQA #1, undecided
'91 200 TQA #2, up in smoke 2
'89 200 TQ, "Bad Puppy", up in smoke

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