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VWDoc, Independent VW Shop owner
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1999 vw: beetle..a/c compressor wont power on..pressure switch

Customer Question

1999 vw new beetle a/c compressor won't power on. checked for power to it. can cross pressure switch nothing. replaced fan relay same thing. checked fans work perfect. i can manual power on the fans and a/c clutch on the relay by applying power to the fan relay with putting power to the 2 green wires. one for fans and one for relay. works great then but then car is idled too low. so do i need a computer? or is something else telling the computer to cut the a/c off? thanks
Submitted: 5 years ago.
Category: VW
Expert:  Peoples Car replied 5 years ago.
Hi crushir... If the freon is low the computer will tell the relay to keep the compressor off.
Customer: replied 5 years ago.
yeah thats elementary...... if u jump the pressure switch it will take care of that issue no matter what still nothing. the pressure is perfect also i have more complicated problems.
Expert:  VWDoc replied 5 years ago.
Ok, the first thing I need to know is which engine you have in your Beetle. 2.0 gas or 1.9 diesel?

Also, can I assume that you either have a multimeter and/or a test light?

And, when you say fan relay, exactly which relay do you speak of? The one under the battery tray area?
Customer: replied 5 years ago.
yes fan relay under the battery tray. 2.0 gas. i have traced it down to the three green wires that wire into the relay. two of them have 12v when the a/c works one makes the contact come on for the fans and the other makes the contact for the compressor. when the a/c is working i have 12v at both of them. when it quits i loose 12v on them. i can apply 12v to them manualy and works perfect. just then the car is idled too low. something is telling the computer on the car to kick the compressor out and i can't figure it out. Pressures are perfect. both fans work. this has been going on for about a year. was working on and off now it won't work at all. you can unhook battery and it will reset it. will them work for about an hour or so. then do it again.
Expert:  VWDoc replied 5 years ago.
Ok, good information.

I'm going to need more though.
I need to know what the high and low side pressures are at the moment the compressor shuts off. You mention a low idle problem, which can obviously allow the low side to drop under the specified pressure to keep the compressor running.

Also, the wires you mention, can you please tell me exactly which wires (are there any tracer colors), using color coding, or even better, pin designations (1-14), as now that I'm looking at the wiring diagram, I see multiple green (no tracer) wires.

I'm also going to need you to check for power across the ambient temperature switch (right side cowl, under plastic cover) and the A/C cutout thermal switch (in water pipe, ahead of the blue coolant switch), as these are in series with the A/C pressure switch. Obviously, this will have to be done when the compressor clutch is NOT working.
Customer: replied 5 years ago.
thanks for the help so far. vw has been telling me there no other ac switch other than the one that screws in the line. can i jump the ambient and the a/c cut out switch to check to see if thats it?
Expert:  VWDoc replied 5 years ago.
It's definitely worth a shot. As I mentioned, these other switches are in series with the pressure switch, so make sure you've got power to pin 2 on the pressure switch first (blue/red), then the circuit is closed to the control module through the other switches, and finally grounded at pin 8 on the module.
Expert:  VWDoc replied 5 years ago.
Have you performed these tests?

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