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Air conditioning failure - clutchless/variable displacement compressor failsafe in pulley?

the sheep on Wed April 15, 2015 9:31 AM User is offline

Year: 2003
Make: Audi
Model: A6 C5 Avant
Engine Size: 1.9
Country of Origin: United Kingdom

The AC has stopped blowing cold on a 2003 Audi A6 C5 1.9tdi AWX. After a lot of internet searching and car poking I think I've found the problem. Any help confirming it would be excellent!

It's a Denso clutchless compressor, is the bolt in the centre of the compressor pulley supposed to rotate with the pulley?

Based on some of the info at the following link it appears that for clutchless/variable displacement compressors the pulley has a failsafe so that when a torque value is exceeded (eg the compressor is jammed) it breaks some rubber component so that the pulley can continue to rotate and not cause further damage. I'm guessing that the bolt in the centre would be directly attached to the compressor shaft and it not moving with the pulley indicates that the compressor is no longer being turned, hence no cold air. If anyone can confirm that before I buy another compressor it'd be great!

Video showing pulley and bolt with engine running:

Image showing pulley stationary:

Background info:
The only VCDS faults in the HVAC section were for a faulty air quality sensor - I didn't see how this would stop the AC
I've had the car for a year, I'm not sure if the AC was ever serviced before (now 12 years old).
Late last year the cap on the front of the compressor pulley fell off, I found it and the securing bolt on the engine cover and refitted and the AC worked again fine, it then fell off for a second time so I put some thread lock on it and did it up tight. It's been fine until last week!
The electric auxiliary fan does not run, there is power to the connector but the fan doesn't run - I think the fan is toast but doesn't look to difficult to replace (eurocarparts have EIS ones for ~£50). I don't think this is the reason for the AC not running - I would have thought that the AC would turn on for a bit before cutting out, I've tried running the AC on the motorway where there should have been plenty of cooling flow and it still didn't work.
I had the system regassed initially, it didn't work but I forgot to ask whether there was already pressure in the system before they tried to put new stuff in.
The econ light goes on and off fine - doesn't seem to indicate a failure with the low pressure switch or the system being low on gas

mk378 on Wed April 15, 2015 11:03 AM User is offline

Yes the bolt and the center part of the pulley are on the compressor shaft and should turn all the time. Sometimes the breakaway happens falsely even though the compressor itself is not seized. Having a condenser fan not working leads to excessive pressure and compressor torque-- you need to fix that.

the sheep on Wed April 15, 2015 12:28 PM User is offline

This may be good news, is it the 4 pins shown around the bolt that breakaway? If so potentially I could replace the auxiliary fan and then just fit a new cap on the compressor. Something like this:

If not it also seems possible to replace the complete pulley:

I guess the risk here is that the compressor has actually failed and it does need replacing. I would potentially be running it a bit more and potentially sending swarf around the AC system. I guess you'd hope that if that were the case the break away system would breakaway pretty quickly.

My uneducated view is that it's worth taking a punt on one of the above options. Thoughts?

Jag987 on Thu April 16, 2015 2:05 AM User is offline

If the break away points failed and not the compressor, then yes it would be possible to just replace the pully assembly. Try to turn the compressor using a wrench on the center bolt, it should turn quite easily. Here is a picture of a VW compressor that did fail and the break away points broke as designed. Notice that the center bolt is also broken, it did not turn when tried by hand and broke off.

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

the sheep on Thu April 16, 2015 4:36 AM User is offline

Thanks for all the information.

One thing still puzzles me, if the rubber/plastic component has failed wouldn't the whole of the front plate remain stationary when the engine is running? In the video linked in the first post you can see the front plate moving with the pulley while the bolt remains stationary.

The only explanation that I have for this is that I've separated the splined section of the front plate that connects to the compressor shaft from the rest of the front plate. The front plate seems to be made of two parts in this replacement part

In the diagram shown on another thread on this forum ( there are two washers that seem to sit between the front plate and the compressor axle. When the front plate fell of in the past I replaced it and the bolt which I found in on the engine cover but I was not aware of any washers. I'm thinking that if I missed the two washers and did it up tight (which I did to try to avoid it coming off again) I may have put stressed it more than intended and broke the plate rather than the plastic component.

Am I making any sense?
Have you guys seen the two washers?

If the above is correct and the compressor isn't seized I may be able to just replace the front plate... which would be excellent

the sheep on Fri April 24, 2015 6:51 AM User is offline

Seems to be solved - here's the update for anyone else with similar symptoms.

I replaced the auxiliary fan with an EIS one from eurocarparts - it doesn't seem as decent quality as the oem one that came out of it but it's easy to keep an eye on. The new fan now runs whenever the econ light is not lit. You can tell it's running when outside the car by the noise and I don't remember hearing the old one run for a while. Fitting it was a bit awkward but I didn't bother moving the front lock carrier into the service position. Would have been easier if I had but it was quicker this way. I removed the front section of the air intake, the top section of the timing belt cover and the bottom engine cover (just to route the power cable).

Compressor pulley
The front plate on the compressor pulley had not sheared. It turned out that the splines had been stripped. I think that they partially stripped the last two times that the plate worked it's way loose and there wasn't enough left to hold up.


The mating splines on the compressor shaft appeared to be fine (must be a lot harder) so for now I've just replaced the front plate with this one and it's all running cold again. Removing the old plate was difficult because turning the bolt on the outside just span the compressor shaft (the plate didn't turn with it so you can't hold it still). I connected a socket up to a drill ran in reverse to get it off. I had to lower the compressor to get access to the pulley bolt with the drill.

I'm hoping that the combination of not having the aux fan working and the ac gas not having been changed or topped up as far as I can remember combined with the front plate spline being weaken by falling off the axle a couple of times was the reason for the spline failing. Now that it's been regassed (my first step in trying to get it fixed) and has a working auxiliary fan I hope it'll last a bit longer.

If the spline on the compressor shaft has been damaged I imagine that this plate will fail in the same way and I'll fit another £14 front plate and maybe put some JB weld or devcon on the spline. Alternatively it might turn out to be the compressor that was on it's way out the whole time...

Hope that helps someone else out there! I guess the moral of the story is check that your aux fan works and if the front plate from the compressor pulley does fall off, have a good look at the splines before just putting it back on.

Jag987 on Fri April 24, 2015 6:45 PM User is offline

Thanks for the update! So often we never hear what was found or the end result!

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

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