Aircon problem

[ggoodwin]

I'm trying to get the air conditioning working on my son's Mk4 Golf GTi 2.0 1999 V-reg.  I thought that it was just poor because it needed recharging so I took it to be done last week and although it was low on pressure, it didn't cure the problem.

It is a manual aircon system and it turned out that the clutch wasn't engaging on the compressor when you turned on the aircon switch.  The fan also wasn't coming on.

I checked the voltage at the connection on the compressor and I was getting a constant 9 volts when the ignition was off and also when the aircon switch was either on or off.

I then gave the compressor 12 volts direct from the battery and the clutch was engaging fine.

I wanted to check the aircon pressure switch but when I removed the connector it turned out to be a 3 pin version.

I've checked all the fuses in the cabin and those on the battery and all are ok.

I warmed up the car and both the fans came on when it got hot.

I've searched various forums and have found some references to having a constant 9 volts but have not seen anyone posting what actually cured it.

I've also seen about a resistor fix for the fans but I don't know if this is relevant in this case.

1)  Is there any way to check the 3 pin version of the pressure switch?

2)  What could be causing the constant 9 volts?

3)  Could the fan controller be causing any of this and is there any way to check it?

Any other suggestions would be gratefully received .

Graham

[james2]

What i would of done when i got it filled up is have it serviced.  .I would look into getting a new 3 pin switch if that what works it.  I would try kwik fix i think i heard they refill and do a service on them.

[ggoodwin]

Well, I think I did have a service as that's what they called it but, I don't really know what that includes, obviously not getting it to work!

I wasn't sure if there was a way to check if the 3 pin version was working correctly or not and if it failed could it cause a constant 9v supply to the compressor.  Or is there something else that could?

Thanks for the suggestions .

Graham

[AaronGS]

Hi Graham,

I had a similar issue last year. I trawled lots of furums loking for answers and none of the suggestions worked.
I did manage to test all the plugs (like you are trying - there is a good guide over on uk-mkivs.net. Search for fan control problems) and that didn't solve the issue.

It turned out that my fan control unit was shorting out. Its the little black box that sits under the battery tray. Battery has to come out to get at it. That little box costs about £120 from Vw or you could try to get one from a scrappies yard - they seem to be about £15-20 from them.

Thats solved my problem.

Good luck.

Aaron

I think how to test it may have been in this thread somewhere:
http://uk-mkivs.net/forums/p/59897/905449.aspx#905449

[ggoodwin]

Hi Aaron,

Many thanks for the info.  If I can't find the answers in the thread you've linked to then I'm probably not going to find them at all .

I'll settle down for a good read later on.

Thanks again.

Graham

[ggoodwin]

So, I really did read the whole of that thread and picked up a lot of useful info.  I still haven't quite fixed it yet though.

I tested the fans by shorting the plug and they both worked on low and high speed so I ruled out the internal resistor being the problem.

I removed the battery and accessed the fan controller.  I tested all of the inputs and outputs based on details linked to in the thread and all those I could check seemed to be operating normally.

The testing of the 3 pin aircon pressure switch is a bit more of a problem.  It looks as though you need an oscilloscope and a degree in electrical engineering to test it properly and so I drew a bit of a blank on that one, having neither.

I decided to change the fan controller based on the fact that the fans weren't working and it was cheaper and easier to replace than the pressure switch.  It wasn't the fan controller.

So as far as I can tell, I'm left with the aircon pressure switch as being the culprit and the only way I can check it is to change it.  It is obviously a bit more of a complicated mechanism than the 4 pin type and so I could well believe that it might produce some odd results if it went wrong.

As it could cost about £40 to buy, I just thought I'd see if anyone had any thoughts/knowledge on whether this device going wrong could cause me to have a constant 9 volts at the compressor and, in turn, stop the low speed fans from coming on?  Or is there still some other component in the system that might be the problem?

I'm prepared to change it on the off-chance but I hate that feeling,as with the fan controller, when you replace what you thought was the faulty part only to find that it wasn't!

Thanks for any insight.

Graham

[ggoodwin]

I know it is bad form replying to my own post but, in the interests of sharing info, I found a pressure switch for £15 on ebay which was the same part number as mine but had obviously had a design change.

I fitted it this morning feeling rather pessimistic but I'm pleased to say that it cured the problem .

So, if anyone else is experiencing low voltage to the aircon compressor and the low speed fans not working when they will work with a direct power supply, then I'd recommend trying a replacement pressure switch .

Graham

[Wazzzer]

common fault mate, replaced mine a few years ago

[ggoodwin]

common fault mate, replaced mine a few years ago

Yes, but the symptoms didn't seem to be common as no-one seemed to know what was causing them .

Graham