divil

My air conditioning hasn't worked in a while. It blows air at the ambient temperature. Some time ago I asked a mechanic to look at it while doing some other work, and it wasn't fixed. I noticed the invoice bore the cryptic message "a/c - needs wiring" but at the time I was too busy to look into it.

Anyway, I'm going after it now. The clutch does not appear to engage. I presume I'd see the part in front of the pulley turning if the clutch worked? It's not turning. I pulled the relay and tested it, it's fine.

So then I read in this thread that apparently you can test the clutch by shorting the green single-wire connector in the cluster by the PS reservoir to the battery. When I do this I get nothing. No sound at all, and if the engine is running with air con switched on, the compressor still doesn't engage.

Am I testing the clutch correctly? I am hoping this just means the wiring from the connector to the compressor is bad...

SloopJohnB@mac.com

Hard to say if you got the right wire...you're looking for the wire that goes to the AC compressor clutch and there are probably quite a few green wires up by the reservoir.

Much more likely is you have low refrigerant.....find the low refrigerant switch and short across the two terminals at its connector for a couple seconds...if compressor clutch kicks in you have low refrigerant.

Get a couple cans of R134A+ or similar and charge the system...follow the instructions on the kit.

Clearly, if you look at the ac compressor and see a wire dangling from the compressor...the wiring needs to be fixed, but otherwise there's the procedure. BTW, the switch on the compressor is most likely the high pressure switch...it's always on unless HP switches it off. The LP switch, on the other hand, is always off unless refrigerant charge above say 10PSI? turns it on...

Highly unlikely the wiring from the connector to the compressor is bad unless a rodent chewed it or someone otherwise damaged it.

4Driver4

Not a common failure. More likely low on Freon due to leak.

VAG-COM output tests should be able to test the clutch, IIRC.

4Driver4

I agree with your diagnosis, but not your solution. If low refrigerant, leak should be fixed prior to recharging. Also, Audi specifies a measured charge.

divil

tNope - there are a few wires sure enough. But the one I used was the only one that matches the description I read, which was that the connector was green and had only a single pole - the rest all have several and are different colours. It does look like it goes to the compressor but I haven't got down under there to make certain yet. It's very very messy down there from years of oil leaks. According to the guy in that other thread I linked, you can force the clutch to engage with this wire even if the pressure is low.

It was the mechanic's comment that made me go looking at the wiring etc. in the first place - I presumed if it just needed a recharge he'd have done that. But you never know I suppose.

I'll try the other tests anyway, maybe I'm somehow not testing the clutch right. Thanks!

SloopJohnB@mac.com

All true...but all AC systems leak to a certain extent...on a ten year old car it's not unusual to have a low charge.
And yes, Audi specifies a measured charge...but I've used
http://www.amazon.com/EZ-CHILL-R134A.../dp/B004BSNNY2

and it works great. Just fill it up until the AC blows cold and perhaps a 10-20 seconds more (fill it up from the low side which is under the plenum cover on the passenger side between the battery and the pax side of the car.

For awhile I was going to the dealer under warranty every summer and they couldn't find a leak...even my electronic leak detector on high sensitivity wasn't triggering when I checked the evaporator. Dang dealer said they vacuumed and charged the system but by next summer it was blowing warm again.

I've used the chill 134A+ or some variant for some three years now...haven't had to recharge the system for two summers...this is the third one coming up.

SloopJohnB@mac.com

Well, you can check the continuity of the green wire to the AC clutch....if it's the right wire and you don't get compressor action, then you have a bad ac clutch.

most people just replace the entire compressor assembly...replacing an ac clutch is special tool time, service position, etc.

divil

ok - I just checked the wire - I definitely have the correct one. I wasn't able to check for continuity down at the clutch due to it being hard to see and too hot right now to poking around. I might have to raise the car up for that after it cools down. But I can confirm it's definitely right the wire I was connecting to the battery, and nothing was happening when I did that, regardless of whether the ignition was on, off or the engine running.

divil

I had to leave this for a few weeks but just now I recharged the low side using a DIY kit. I know it might not have been the best move but I haven't had a chance to get it to a mechanic yet and curiosity got the better of me

Anyway, the pressure was down to around 15 or so, well below the green level. I followed the instructions and charged it up to the top of the green zone on the gauge, around 55, with the engine running. The compressor still doesn't engage. I can hear a click when I switch econ mode on and off, which I never noticed before - it sounds like the clutch relay. But I still can't see the clutch turning and still don't get cold air

SloopJohnB@mac.com

I spoke too soon...just had to dump a 16 oz can of 134A+ into the 2K4.2A6. Blows cold now.