AC Compressor not engaging

[malc350]

My AC compressor on my 90 is not engaging. When I go through the AC diagnostics the only fault code I get is 09 (low freon level detected).

When I took the car to the air con shop the guy connected my car up and said my car is holding pressure but the AC compressor clutch is not engaging - that's why my air isn't working.

I have a feeling there's nothing wrong with my AC, - it just needs gas (?) The mechanic said I could bypass my pressure switch but as far as I can see I have three pressure switches on my AC lines so which would I bypass?

The AC hasn't worked as long as I've owned the car - just over a year (I know I should have attended to this earlier) - but I'm sure I've seen the compressor engage before. The clutch isn't seized because I can turn it by hand.

Any help would be appreciated. Thanks, Malc.

 

[Robertwav1]

First things first. I assume it R-12 and not a conversion to 134a. Hope I'm correct here. The system generally holds approx 1.75Lbs to 2.0 Lbs. gas. I don't use this to charge but it's a general Idea. The low pressure switch should be made if there is enough pressure in the system. I usually charge a 12 system approx 34 to 40 Lbs. on the low side with the engine RPM around 1000. Of course it depends on ambient temperature. On a hot day pressures are going to be higher, on a cooler day the other way around. Before anything is jumped out make sure ther is enough gas in the system. Static pressure on a hot day for 12 is around 120 Lbs. We'll go from here...

 

[jsinga]

Holding pressure means you don't have a BIG leak.
If the system pressure is low enough the low pressure switch the one just in front of the evaporator box will keep the compressor from engaging.
If you jump the terminals of the low pressure switch in the plug and everything else is working you will get the compressor to engauge.
If you want to know it the compressor clutch is good unplug it and jump 12v to it and it will lock up.

JS

 

[malc350]

AC on 90 Vette

Hi guys, thanks for your replies.

I had the system charged yesterday and my AC works fine (fingers crossed - there's always an element of doubt when it hasn't been running for a long while).

After much investigation it turns out that the compressor won't run as long as there's an AC fault code stored. I had to get the shop to charge the system slowly with the compressor not running, disconnect the battery for 1 minute, reconnect and hope it all starts working again and that's what happened!

BTW due to the fact that R12 is no longer available I asked the guy what gas he was going to use and he said R24a which is a direct replacement for R12.

I've never heard of this gas - don't know if it's a UK only thing or what. I know it was dearer than R134a (they had that gas for newer cars)

Regards,

 

[mjlisz]

Hi,

I just had a similar problem with my A/C. It turned out that the gas was leaking from the shrader valve where you connect the A/C guages. This "leak" would not show up with gauges attached. Upon further investigation, someone on an A/C discussion forum said that shrader valves themselves are not considered leak-proof by Chevy. You need to have the caps on them to be leak-proof. Take this for what it is worth, but make sure you have those shraders capped to prevent further leakage.

Mike