So my ECON button got stuck in the on position on my 2004 Audi 1.8t avant, and no cold air so I assumed I was low on refrigerant and it went into safety shutdown. I refilled it with r134a with UV dye and it would hold for a little bit, but then quickly empty. Even with the UV Dye, I couldn't find the leak.

I put it on the VAG Com and got a high pressure side fault, which as far as I know, just means that it's out of r134a.

Then I got the bad news, the compressor is getting power to it, but will not turn on, even when there's the proper amount of refrigerant in there. So leak or no leak, the compressor seems bad.

Here's where I need some expert advice: I ordered a new compressor, and based on my vin #...E74A239... and according ECS Tuning's site, I need the denso model. Which is what I bought.

I went to bolt it up last night and I saw that, although they're very similar, it's slightly different from what is on there. The compressor currently on the car is a Behr 8FK model. The electrical plug and line hook ups look the same, but I don't want to swap them out until I confirmed that this new one would work. For all I know, the previous owner may have replaced it with the wrong one (Behr compressors were on 2003 models, mine is a 2004 A4 avant).

How can I be sure which is the proper model for this car? And or are these compressors interchangeable?

 

What if i told you, you have variable output compressor...? Which means its ALWAYS on. So the fact you have power to the compressor but no operation doesn't mean you have a bad compressor.

You have a leak. Leaks tend to come from one of the the two weakest points. Either the condensor or the evaporator, unless you broke or pinched a hose somewhere. Finding leaks are very hard sometime, Using dye makes it easier but still can be difficult sometime. The fault it there because of either low or high pressures. You have no way of knowing your charge unless you have one of those expensive machines. They not only tell you how much you take out but vacuum tests the system for leaks as well. And you can be exact in what you put back in. Those bottles you buy from Autozones are really just a waste of money.... because you need to have an understanding of the current operating condition of the system before you can properly diagnose it.

Compressor wise.... two car of the same year and engine can have to different compressors. Same goes with alternators. You put the one that you take off as rule of thumb

 

Replacement parts don't always look the same, but as long it it fits and works then use it. You can find a leak buy presurizing the system with air and spraying down places where it could leak with soapy water. You'll see bubbles if there's a leak. You may also be able to hear it. It could also have been the compressor leaking.
Regarding the compressor, most will not come on it the refrigerant is low.

 

Audi Tek & BigDogg,

Thanks for the replies! I agree I was way out of my league as far as AC repairs go, which is why I took it to my local german repair shop in town.

The system would hold the proper pressure for a time, and even then the compressor would still not operate. So with the proper amount of refrigerant and power to the unit, there still was no joy. So even though it is a variable output compressor (which I did not know, thanks for the tip!) I'm assuming it's still possible for the compressor to go bad, and I think in my case, it indeed did fail.

What was tricky was the compressor on the car was a Behr / Hella unit, which I found impossible to find. What was called for with that model and vin number was a Denso unit. So that's what I replaced it with. The designs were similar, but not exact. So when we were installing it, the lines didn't match up to the new compressor. So what we ended up having to do was remove one of the manifolds on the old and, and swap it out on the new one.

Then we changed the dryer to be safe, did a nitrogen test, which seemed to work just fine. Then we refilled it with 134a, and now has been working perfectly.

As you said, even with UV dye, there still maybe a leak somewhere that may be going undetected, but so far so good.

So, going forward, if anyone has a bad Behr / Hella compressor at some point, it's replaceable with the Denso unit, you just have to swap out the manifolds.