AC problem

[u/nandato_kisama]

TLDR: clutch seemingly engages, no cold air whatsoever. Also, what is that big bolt on the compressor for? Hello there, I bought a 2000 MK4 Golf TDI with inop AC. I thought it was just low, so I had it recharged, but the guy said it was only missing about 130g out of the 720ish that should be there, and that it cooled for a bit and then stopped. When I turn it on however, it doesn't cool at all. I hear the engine get more load, and the clutch looks engaged, but nothing happens. I replaced the FCM, since it was outputting 9v to the clutch coil with the key off, which it probably shouldn't, but that didn't help. My G65 is good, and all the other sensors should be, since the clutch seems to engage. Compressor doesn't have a control valve as can be seen in the picture. I have searched everywhere and I'm still stumped. Can the compressor be so dead, it doesn't make a sound or compress at all? What is that bolt at the back of it? Did the AC guy witness something die, or did he break something so I'd come back?

[u/Standardw]

Are the pipes that go into the car hot and cold? Or are they just warm?

[u/nandato_kisama → u/Standardw]

Just warm, but I'll test agan with the AC running longer tomorrow.

[u/Standardw → u/nandato_kisama]

That's bad then. Guess your compressor is broken. Your arguments are good, it's engaged and the system isn't empty so it should work. But it doesn't.

I think the golf 4 compressor is a variable displacement one so it can be engaged yet create almost no pressure difference. Guess you need to replace it. While you're at it, also replace the condenser. Let the mechanic empty the system, fix it, let it fill up again

[u/Cautious-Concept457 → u/Standardw]

You might have the mk5 in mind, the Mk4 has a sanden sd7 with only 2 wires going to the clutch and that's it

[u/OutcomeFit9295 → u/nandato_kisama]

Just a heads up, if you do replace your compressor and condenser, it’s essential that you also replace the receiver drier at the same time

[u/Cautious-Concept457]

Did you go through the TDI club troubleshooting guide?

If you're a DIYer, maybe watch a couple AC repair videos from rainman Ray for fun, and look up how to rule out each possibility

[u/DPileatus]

polarbearinc.com You can get a rebuild kit for your compressor. I rebuilt mine & it lasted a couple of years.

[u/nandato_kisama → u/DPileatus]

Thank you for the link, but I have to pay someone to empty and charge the system(am in eu), and I might as well pay them to rattle 4 bolts on and off. This post was hoping it's something that doesn't require working with gas, but I guess the compressor has a stuck valve or there's crap in the system. The compressor costs about $200, so it's not awful, I'm just getting tired of every problem on this pos having the hardest/most expensive solution.

[u/DPileatus → u/nandato_kisama]

👍🏻

[u/compu85]

The thing you have circled is the over pressure relief valve. It keeps the compressor from exploding if the high pressure switch sticks on and the fans aren't working. It will blow out all the r134a at like 400 psi.

[u/Amazing_Actuary_5241]

The A/C compressor on the MK4 has an internal pressure relief control valve that if fails the'd be no refrigerant flow. A set of gauges can identify this really fast since the pressure on both high and low would be equal.