Guys, I have an old 1998 A6 avant 1.9TDI with nearly 150k miles on the clock, that has been a joy to have, however I now have an aircon problem. The system is fully gassed with 134A however the AC compressor is not kicking in. I have no schematics of the wiring and am therefore at a loss to do all but the most basic diagnostics (fuse testing). The manual mentions fuses 3, 5, and 15, all of which are good, but I'm surprised the AC clutch isn't mentioned. The thermoelectric fan is also not cutting in, but to be honest the engine runs quite cool most of the time. Are there relays, switches or whatever that I can check that I may have missed before I end up taking it to the money pit that is my local Audi dealer? I am driving down through France this week and the thought of my kids moaning about the heat all the way down..........Any ideas greatly appreciated.

 

There are so many things that can cause the compressor to not engage. There is the CC head unit itself, the low pressure and high pressure switches, the wiring to and from the compresor, the compressor thermal switch and just a plain worn out compressor. There are also 1 to 2 relays, the fan relay and the compressor relay. The first thing I would do is hook up your manifold gauges (you have them right, don't work on AC without them) then jump your compressor to the battery to force it to start. What do the gauges say, if everything is within normal ranges, then check your high/low pressure switches. You can jump the low, see if it engages the compressor now. The fan generally does not turn on until the compressor turns on.

Please provide more specific troubleshooting, how do you know the system is full. Jump the compressor, jump the low pressure switch. Report back.

Jeff

 

Jeff
The reason I know it has a full charge is because I've been overseas for the last 7 months and when I came back my wife had been running around with theCC on Econ. I thought the obvious snag was a loss of charge from dry compressor seals, however my local charging guy recovered0.84kg and put back 0.85. That's how I know I have a full charge and a tight system, but before delving too deep I just wondered if there were any easy fix problems before I take it to Audi to look at. The AC was positively Baltic before I went away but someone told my Mrs that if you run it on Econ it saves on fuel. The thing is she was in rainy, cold England quite happy while I was in southern Iraq desperate for a bit of air con!! I'll do as you suggest and keep posted, thanks for the advice Mate.

 

i have the same problem,right now in ny its summer time and i haveno AC,and by the time i save enough cash to get it fixed, winter time will be here

 

Ok, knowing it is full and it basically shut off one day, do jump the low pressure switch first, then try the compressor. If jumping the low pressure switch does not engage the compressor, but jumping the compressor does engage it. Next move to the relays (hook your multi meter up to the compressor and see if it is getting any power). Your a/c clutch relay is # 267, it is located "13-fold relay panel, underneath left side dashboard, trim panel removed" description take from Bentley manual. Your low pressure switch is located on the right side of a/c condensor. Make sure your CC is set to LO, you could even turn on the defrost and rec.

Jeff

 

Jumping either the switch or the compressor made no difference; howeverI've managed to ascertain that there is power getting to the AC clutch but it simply isn't operating, so I'm guessing a new clutch at least will be required. The otherproblem is the fan. This will operate when jumped but power does not seem to be getting to it normally. I've re-checked all of the fuses and they're good so am guessing a further relay problem?? Does the fan run all of the time or does it cut in and out, also does anyone know which relay it is operated from, as this may be my snag. Is it possible that the potential clutch problem could have happened as a result of the fan failing?
Thanks for the help in advance guys.

 

It is possible that the clutch is stuck. Like brushes on an alternator, sometimes they just need a little beating. I agree that the fan relay is probably bad. I believe my electric fan runs continously when the clutch is engaged. But I would not replace it until you get the compressor running. Compressor clutches generally don't just die, they slowly wear out. On my old Volvo 850, I had to take the compressor apart to remove some shims, these shims adjusted the distance between the clutch and the input shaft. What was happening was the clutch material had worn down to 1/2 its original thickness (in 300k miles), causing it to overheat and eventually just didn't turn on because the thermal switch would not allow it. So I removed 1/3 mm shim so the clutch would make solid contact and no longer slip. I also bypassed the thermal switch. Total cost was zero, but it was a pain to get the compressor out.

 

I don't know if Audi uses thermal switches, but that could stop the compressor from turning on. On Volvo's if your thermal switch is bad, the compressor is sent power, but the thermal switch prevents the electromagnet from engaging the clutch. Just a thought.

 

Jeff
having done the basic diagnostics and looked at the clutch job I tracked down a re-conditioned clutch from a mechanic friend of mine. We managed to get the car onto a ramp and he helped me replace the clutch in exchange for my oldone (which he will now re-condition), and the cost of a few beers. The compressor now runs fineand the aircon is working again, however the fan still will not cut in. The inlet side of the condenser gets absolutely red-hot in a short time if the car is stationary, hence the need for the fan. I guess if it was left running like this for long enough eventually the temp would get so high the AC would trip, but I didn't want to risk trying as I'm still concerned this may have caused my clutch to fail in the first place.
As a short term solution,I'm thinking of jumping power across from the clutch feed to the fan temporarily but the wiring to the fan is much thinner than that to the clutch and I'm a little concerned that it may not be man enough to handle the current.
I've got to drive through France in a couple of days and am thinking I could maybe run the AC so long as the caris moving above 30mph. At least my kids will be kept quiet!!
I'm now going to try andfind the fan relay and see if it's operating. If I need to replace it, it will have to be after my holiday.
Any thoughts?

 

Our bmw's electric a/c fan died a long time ago. We should replace it but, anyways the a/c works just fine if we keep it on the hwy. When we get in the city we shut it off if we are going to be sitting at stop lights. Your right about the lack of fan probably burning up your old clutch. Heat kills clutch material really fast and I have learned that Audi I don't believe puts thermal switches on thier clutches. So a compressor could wear out its own clutch real fast. I am not sure where the fan relay is, but you could try jumping the relay itself. It would cause the fan to always be on, but that is not a big deal as a short term solution. Glad to hear the compressor is fixed. It would be a far better idea to have the fan running, even if you have to run a couple wires from the battery directly to it just to make sure the ac is getting air flow. If it does overheat, not only do you risk ruining the compressor, you risk blowing o-rings. More than likely thought the high pressure switch will shut it down before damage would be done.

Jeff