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Air con compressor not engaging

Mark Elder

Mark Elder

PCGB Member
Member
Just had the "free if we don't fix" KiwkFit aircon job done.

It was free[:(]

Good news is their machine said "no leaks" and indeed (4 years after last recharge) it still had 500 units of pressure. Which the guy said meant it was pretty good. He topped it up to the 800 odd it is supposed to be but that had no impact on the temperature.

His kiwk-and-dirty diagnosis is that the compressor is not engaging - because there is no sign of pressure change in the system when he would expect it to kick in.

So either there is an electrical fault or the compressor clutch is toast.

Any investigation I can do, or should I just start looking for someone who understands 993 aircon?
 
Hi, did the ac work before qwik fit played with it? If it did it but it doesn't now, it could be that they over gassed it, 993s use a lower charge of gas than a lot of other cars. Plus did they realise that as well as the ac button being switched on the fan switch on the ccu has to be turned to at least setting one or the ac compressor will not kick in. If you could supply a bit more info on when it first stopped working, has it ever worked since you had it, was it ok before kwic fit gassed it etc, then myself and others on here can give you some more advice on what might be wrong and how to test it.
Hope this helps, cheers
 

ORIGINAL: Mark Elder


So either there is an electrical fault or the compressor clutch is toast.
Click to expand...

My guess is electrical.

First check the fuse

second check if you can hear a 'Clack' when the clutch engagaes.

If you hear a 'clack' the clutch is faulty, but if you don't, the problem lies between the fuse and the clutch solenoid.

You will need a wiring diagram and a simple test lead to determine where the fault is. Maybe it is the thermostat, but who knows until you start tracing wires.

Have fun !
 
You will be able to see when the clutch has engaged since the shaft to the compressor itself will be turning when engaged. The belt over the outside pulley will be turning all the time that the engine is running, but it will appear to be freewheeling when the clutch is disengaged.
 
And one thing that will stop the clutch engaging is if the system thinks there is no pressure. So you might have a failed air con gas pressure sensor.

Ian.
 
ORIGINAL: Ian McLeod

And one thing that will stop the clutch engaging is if the system thinks there is no pressure. So you might have a failed air con gas pressure sensor.

Ian.
Click to expand...

Or more common, a failed gas TEMPERATURE sensor.
the easiest way is to read the fault code stored on the DME.
my guess it's the inside evap temperature sensor.
when they give up, they give a reading of 300 * celcius and the clutch will never engage.
part wise it costs 30 ish and is located under the front hood under the wipers up in front of the evaporator. (under the black plastic cover) 96461894300
to change, you have to solder the wires of the new temp sensor to the harness, and isolate with electric tape.
very easy.
 
Thanks for all the ideas guys - looks like I shall be having fun with the multi-meter.

The air con has not been as good this summer as in previous years and I kept meaning to get it topped up. Then in early September I was realising it was not really working at all - so I suspect this fault was not caused by kiwkfit and actually happened as a result of being layed up and unused all of August while I was away on holiday.

Perhaps there will be an aircon expert at tomorrow 993 meet in Halesowen[;)], see some of you there.
 
Hi

I hope I'm not breaking any forum rules? But there are some good air con guides at the following links.

http://forums.rennlist.com/rennforums/993-forum/351059-complete-a-c-diagnosis.html

http://privat.bluezone.no/toreb2000/ccurepair.html

Well worth a read for air con info....hope it helps with a diagnosis for you.
 
As stated on Rennlist, these are the relays that stopped my air con compressor from running. It was actually the fog light relay that wasn't working, hence my fog lights weren't working either....check both relays though. You can source replacements from Audi for less than the Porsche version from an OPC:

"Compressor relay "" engine compartment fuse box driver side.
The relay engages with the lead from the fuse to pass current to the compressor relay.

Fog Light relay "" front trunk fuse box
It has been reported that the fog light relay is in a daisy chain config to the compressor relay. If that relay fails, no power will pass to the compressor relay. To verify your relays, you can switch with other relays that have the same part number."
 
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