Mark 5 2.0 TDI (2008) Air con issue

[DWBN]

You don't need to touch anything apart from the compressor if it hasn't already failed. Replacing the condesor and reciever dryer will only be required if the compressor has failed and sent swarf through the system (most common in the denso units).

[Idle]

If the compressor was dying I think it'd have blown before now — that it's working so well suggests it's OK.

I'd check the electronics first — something's causing that excessive load and it shouldn't be anything mechanical.

Could be a valve not opening, perhaps (note I'm not a refrigeration expert.)

[harlie]

hi folks
I would appreciate some insight into an air con issue I have. I noticed it was slow to go cool - like 5 - 10 minutes after which it was OK but not icy.
My service guy says the compressor is only making 11-12 bar and is probably worn out. Car had done 140K kms, not a lot I would have thought.

Dies this sound right? And I am told just $1200 will set it right again.

Any comments will be very welcome
Cheers
Geoff

If it is slow to get cold as opposed to not getting cold at all I have some good news. (this may apply if yours doesn't work at all but it is harder to confirm). You have a Clutch-less Variable Displacement Compressor (VDC) - check that when you turn the AC on and off that there is no clutch engaging/disengaging to confirm.

The VDC is permanently engaged, it has an internal “wash board” that changes angle which in turn alters the length of the piston stroke varying output from 2%(required for lubrication) to 100%. The wash board is moved/actuated by refrig pressure released by the Refrigerant Control Valve (RCV) which is controlled electrically by the AC ECU. The problem is the RCV – it sticks (mine was full of crud)– which is why it works after a while and I’m tipping it drops out after a while too. Good news is this valve can be had for $US32 - 80 depending on where from and is located in the back of the compressor. The system has to be evacuated before the valve is removed and regassed after. It is an easy job.

If you are interested I can post up exactly how to tell if your valve is the problem – you need VCDS and about 5 minutes. It will also help if you identify which compressor you have (I got the phone down in there for a photo of the plate).

If the compressor is not working at all the compressor may have a problem with the wash board which could mean it has fallen apart inside - but I bet the majority of owners replacing compressors only need the valve.

I will add that none of the AC shops I spoke to re this a couple months back had any idea - they just wanted big $ to replace everything.

[harlie]

Yep. Ac compressors on vw are not great. Mk5 and 6 had issues. Fitted loads and the always fail your way...takes a while to get cold..when cold not 100% ac cold but is working about 60%. New compressor mate..VDUB...

Classic signs of a sticky valve! New valve is a lot cheaper and requires a lot less labour than a new compressor, which is probably why industry wants to replace the compressor + drier + TX = profit. Not to mention that nearly all the compressors are factory exchange - which means they have a new $32 valve in them and are resold for how much??

[DWBN]

Same problems and I tried the same thing. New TX valve installed, worked for 15 mins then nothing as it was clogged again. While this does work for some poeple, the source of what is clogging the valve in the first place has not been fixed. AC systems don't just clog up. They are a sealed system that should not lose pressure, or have anything apart from the compressor oil and R134. If the TX vavle is sticking, something has entered the system to do so, and 99.9 it will be the compressor failing sending swarf through the lines.

That said, if you catch it early enough a simpled replacement of the vavle will help, but not fix the issue long term.

[harlie]

Same problems and I tried the same thing. New TX valve installed, worked for 15 mins then nothing as it was clogged again. While this does work for some poeple, the source of what is clogging the valve in the first place has not been fixed. AC systems don't just clog up. They are a sealed system that should not lose pressure, or have anything apart from the compressor oil and R134. If the TX vavle is sticking, something has entered the system to do so, and 99.9 it will be the compressor failing sending swarf through the lines.

That said, if you catch it early enough a simpled replacement of the vavle will help, but not fix the issue long term.

the RCV valve is not the same as the TX valve - one is in the compressor controlling compressor output levels (electrically operated and prone to sticking) , the other is inside the cabin before the evaporator acting as a pressure regulator allowing the refrigerant to expand from a liquid to a gas (pressure operated and not prone to sticking but can block up).

RCV = Refrigerant Control Valve
TX = Thermal Expansion

If your TX valve is clogged, that is very different - did you see it? Was it really clogged? I bet it wasn't it just wasn't the problem. You have said you fixed the issue with a new compressor - which means you got a new RCV (it's in the back of the compressor - where the wire plugs in) - So I'm going to stand by my research - you fixed it with a new RCV, the rest of the compressor came for fun.

Do a search for "delayed Air conditioning"on tdiforums, there are hundreds of posts of successful long term RCV valve replacements, the Sanden PXE16 compressors generally don't self destruct like the older Densos, but the RCV is proven to be not reliable. It is a very easy job in the US as R134A can be purchased from the local shop for $11-$12, with a set of $60 gauges they can DIY refrigerant recharge.

Delayed Air Conditioning - Page 32 - TDIClub Forums - BTW the guy on page 32 in Brisbane is not me it cost me 40 for the RCV and 100 to recover and recharge - so it looks like another BNE bloke has had a win. with the car on a hoist it took 3 minutes to change the valve. My valve has a very fine sludgy muck in the filter, there are no metal fragments. Educated guess I would say the muck is oil that's too old and been too hot.

There is a fine mesh filter on the RCV, metal swarf would not get in - However I do agree, if there are metal fragments then you have a compressor internal failure. But that also brings another Question - have you seen a cross section of the Condensor? How does metal swarf get from the compressor to the TX valve, the condenser has galleries that are 1mm in size.

As I said above, with VCDS it is easy to see if the RCV is the issue, a clogged TX would have given very different reading than a sticky RCV. A buggered compressor will give different readings as well.

[DWBN]

Perhaps that is where the confusion is - is the below the TX or RCV? I've changed the vavle in the compressor (which I thought was the TX valve) but with no luck. No swarf in the system either. Weird as it was working flawlessly for the first 30 mins after the swap and regass, then nothing.

[harlie]

That is the RCV - it is possible to get a faulty RCV - they are an electrical item.

If it worked after RCV replacement (if it changed the behavior), I still say the compressor was OK. If the compressor has gone, it doesn't come back temporarily - they fail because the wash board mech breaks, piston rings loose seal, pistons break, conrods break ect - when the compressor fails internally it is a doosy. The Variable output compressors are quite intricate inside (7 pistons!!), but the Sanden units are proving very good.

Next time - and I'm of the opinion there will be a next time it plays up because these valves are a serious week link. Start with your laptop and VCDS to see exactly what the ECU is asking for and what is happening. I have ordered a spare to have on hand when it does go....

[jets]

If you are interested I can post up exactly how to tell if your valve is the problem – you need VCDS and about 5 minutes. It will also help if you identify which compressor you have

I would be interested in this harlie.[I have VCDS] I am not sure if mine is slow to cool as my wife has been using it. I will try it next time I am in it.
Mine is a Sanden compressor. Nos on it 8676f, PXE16,04411809563 & 1KO 8508030. I used a mirror with a remote tilting head.
This means everything is reverse image.

[xradioactiveman]

Hi Harlie , can you tell me where you sourced your RCV from.