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If it was totally empty, I'd be tempted to remove the Schrader valve in the low port, and put the adapter on "permanently." (Should be fine.)

I'll have to see how much is in there, might be just the simple fix, and then it will fill fine with any adapter for the R-134a low side.

Why Audi did not go with a standard fitting is beyond me, but they seem to enjoy confounding what is a great car with little pokes in our eye.

Lucky for me, I have a can of oil/sealant/dye, and a few with just freon and oil. I never just buy the freon only cans, as I agree, you lose oil with the leak, and I'm not sure you can really end up with too much oil in the system by just recharging it every few years. (Any leak I have is very slow, there are no wet/oiled areas that I have found yet, not around the compressor, or the lines/fittings that I've looked over. They are clean and dry as is the rest of the engine/transmission and diff's. (I'm happy to say this car has zero leaks at this time that drip, or are oiled up.)

I've seen the seals leak on compressors that don't run very often, but I've been using the defrost setting every now and then this winter to just cycle the compressor on and off, and of course it works hard all summer long around here.

One thing that did leak was the fan clutch. The stock one failed, leaked, and will soon be replaced now that it's warming up with a cheaper replacement part that seems to be the very same part, but was not dealer priced.

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Update: I've put the new fan clutch in, as the old one was totally worthless, and the fan just turned. (Last summer, in stopped traffic, with the temps near 100f, it would start to overheat the car, with the coolant temps going up above the normal range, if I shut off the ac, or started to move along, it would cool down with the increased air flow, and decreased load on the engine and heat added by the condenser dropping off as the ac was shut off.)

So, the fan clutch works great. Sounds like my S8 wants to take off now, fan noise wise.

But I'm stumped on the pressure switch.

I've got the adapter setup so it will flow R134a no problem.

I've got the can with the oil/leak dye etc. I pulled the lower left fog light surround, pulled the combination high/low switch plug, and tried to jump the plug to get the compressor clutch to engage.

No dice at all. tried many combinations on the plug jumped lines, no deal. Ran out of time, so put it all back together, and will try again, since it was cooler for awhile here in Boise, but now it' hot again, and I need to get this AC system working.

Any ideas/tips on the 2001?

What wires of the 4 for this combination switch need to be jumped?

I was very tempted to just splice into the 12v supply line to the clutch, and hook up my battery charger, sending 12v right into the clutch, engaging it, and screw the picky pressure sensor secret combination.

silverd2

With ignition & AC on, terminals #1 & 2 should kick in the compressor clutch.

But it's not a direct route to the compressor. That signal goes to the climate control head, which in turn, sends a signal to the AC clutch relay under the passenger's footboard. Terminal #8 on that relay (2.5mm wire green w/yellow stripe) sends 12V to the clutch...terminal #2 (2.5mm wire black w/yellow stripe) is the wire to the fuse, #8 3rd row (yellow row).

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Well, I spent some time on the S8 again, and confirmed that there is slightly more than 12v across 1 and 2 at the pressure switch, and 3 and 4 also have just over 12v. The fans come on if I jumper 3 and 4, but nothing happens when I jumper 1 and 2.

So, I pulled the carpet, and floor carpet from the passenger side, and by foot board, do you mean the plywood board that's held in with a few screws?

I did not have time, or want to pull that out unless the relays are behind/under it, and feeling around under that, It looks like just more heater duct work.

Is it a very common thing for the relay to go out? I've seen some stick over time, especially if the ground becomes corroded.

Thanks in advance for any advice, and confirmation of what's under that panel, if anything.

silverd2

Yes, that is the "central electric" panel under the plywood.

If bridging terminals 1 & 2, did not not get a reaction (ignition & AC "Auto" on), then it's worth a search...and a process of elimination.

By removing that panel, you'll also determine if you've ever had water intrusion there...it happens, due to clogged rain and/or AC drains, sometimes leading to electrical (relay) problems.

Bridging terminals 8 & 2, with relay removed (ignition on), should engage the comp clutch...#2 should have battery voltage with ignition on.

If this doesn't work, there could be a problem with the clutch itself or wiring/connection between the relay and clutch.

silverd2

P.S.
That relay panel in central electrics lifts out as a unit with bundle of wires attached, for easier access...it's designed that way.

Risk

This has been such a helpful thread, thanks to all who contributed.

I'm now back at square one after jumping pins 1 & 2 on the sensor pressure switch and also jumping pins 8 & 2 on the relay (climate control head set to LOW / LOW + AUTO and recirc).

Still zero cooling and seemingly no compressor activity.

Is there a recommended way to get 12V to the compressor clutch to see if that is actually the problem?