A/C compressor doesn't turn on

[shellfritsch]

when i press the a/c button, it does not light up and the compressor does not engage. the previous owner said it was working perfectly and the system was recharged - but the van has sat for the last 6 months and i suspect rats might have damaged some wiring. fuse looks good. any tips on how to troubleshoot?

[Jan-Willem]

What I did to troubleshoot mine: I made a copy of the ac electrical diagram. Then with two highlight markers, I marked everything that I know/could test worked correctly green, and what did not work another color. If you have something that works, you can mark every cable/component upstream (towards the battery and the ground) green. I found multiple faults in my AC system this way.
Testing the fuses is a good start, imho looking at the fuses is not. Because you can learn much more by testing them.
For one, a fuse can break without being blown. Especially those clear plastic ones, the pin can come off the fuse wire.
Usually I test with the fuse still inserted, and everything related on. So engine running, AC on.
The fuse has the two small contacts on top. With a multimeter measure voltage between a ground point (any unpainted metal) and the small contacts on top.

12-14v on one contact = fuse is blown or broken
12-14v on both contacts = fuse is good, problem is either downstream, or you have the wrong circuit
No voltage on either circuit = problem is upstream

If there is voltage on both contacts, you then can also measure between the contacts.
no voltage measured, means there is power on the circuit, but the circuit is not actively consuming power
if you do measure voltage(milivolts), something is using power, and you can even estimate how much
https://www.powerprobe.com/na/en/www.powerprobe.com/resources/4Fuse_Charts_New.pdf

You should not forget to check the circuit breakers (racetrack shaped things to the top right of the fusebox, on mine they are black with yellow). Pull them, and measure continuity. You can reset them with a paperclip, but not while powered. Then your paperclip just might turn into a miniature welding rod.

if you are checking stuff on the electrical diagram, another useful and easy check is: listen to the engine when you press the ac switch. Does the engine idle up? This controlled directly from the AC module I think, it is not dependent of the charge in the ac. If it doesn’t maybe the entire ac module is not getting power.
Also I do assume your blower works, if it doesn’t, your ac won’t either.

also, you could try to bypass the ac pressure sensor, or rpm check (by pressing the throttle a bit) but I do not think that is your issue, because I think both would stop the compressor from switching on, but the Ac light should go on.

[shellfritsch]

thank you so much! this is a perfect guide to troubleshooting. really appreciate it.
yes, the blower is working and when i press the A/C button there is no change in the engine idle.

i did try swapping the A/C fuse with another that had the same rating and that had no effect - but i will test with a multimeter.

did not know about the circuit breakers - will investigate. from a quick look in the service manual i am seeing A/C related relays, but no breakers. can you elaborate on which units i should inspect?

fwiw, the rear blower light does come on - no A/C activity though.

[Jan-Willem]

12806
There are two breakers right above each other, but i could not get both in one picture. I think the top one does the rear blowers.

[Jan-Willem]

A bit to the right of the top circuit breaker, are two more fuses, one for the magnet clutch of the compressor, and one for the condenser fan. You can only see them, if you remove the glove box.
but i don’t think these will cause the front ac light, not to come on. Maybe the ac button is broken/disconnected?