MK4 Air Con Saga & Fix

My Golf is a 1.8T Anniversary (petrol) model. Got approx 86k miles and all was well with the world until April this year. The I needed to use the car park called the M25 a lot and the weather got warm.

No worries, I have climate control, just set the temp to something comfy and sit back and watch nobody move for 30 minutes. Strangely, I started to get hotter and hotter, although the car temps were fine. Outside air temp was into the mid-20s, climatronic was set to 18C but I was baking gently. Set climatronic to LO and lots of fan noise and hot air erupted from the vents.

WHOA! Too hot! What's going on? Turned 'off' air con, set fans to low speed, opened windows and fumed!

Finally got to destination and after drowning myself in a sink of water, thought about looking for the problem. Couldn't find anything obvious, so decided to get a regas.

£65 poorer, but slightly cooler (not much), I journeyed home. Still hot outside and warm inside despite 'new' refridgerant, it suddenly got extremely cold, with cold air pouring out of the vents. Thought, 'ah, a blockage that has now shifted' and was happily completing my trip home. However, I did notice that just before getting home, the cold air stopped. Assumed that it had cooled the interior to the required level and thought no more of it.

Next week, same trip to Essex, same problem occured. Began to think the car didn't like the M25 (which I don't blame it), so on my return, took car to local garage for investigation. Admittedly, they are not VAG and not air con specialists, but they are very knowledgeable and will admit defeat before charging you an arm and a leg. They checked codes (none), air con fill (within range 750-800 gms), relays and fuses for open circuits (none - I'd already been there) and finally clutch operation at the compressor (working).

By now, the weather had reverted to normal (carp), so air con was not a necessity. However, demisting was and dry dehumidified air is a definite benefit! Replacing the air con compressor in my GTi is a major evolution and requires much dismantling to get the unit out as the alternator and injector rails are in the way on the top of the engine and the steering pump on the bottom. Either way involves disturbances to other systems which is not a clever way to design things (I work in aircraft design) as it always introduces additional faults and maintenance work.

During this time, the air con would continue to trip in and out at will if I had the temp set low (19C or 'LO' on the climatronic), but would usually stop itself after a few minutes.

At the beginning of July, I was on holiday and the annual service and MoT were due to be done. Decided to get fault fixed and booked into local VAG dealer. After much scratching of heads and phone calls to Milton Keynes, it was determined that the compressor was fine (we knew that), the air con fill was ok (we knew that too), the electrical supply was ok as were the high and low pressure switches (I didn't know that). Therefore it had to be the radiator fan ecu. The what?

Apparently when the air con compressor runs, the radiator fans must be switched on too. If they don't, then the compressor is prevented from operating. This is controlled by a signal from the climatronic to another box of tricks that turns the radiator fans on and off as required. Mine was doing its own thing and having thrown its toys out of the pram, could not be relied upon to work when needed. Unit was replaced for a total of £277 which included at least 8 hours of diagnostics, so a veritable bargain in my opinion.

I have no idea where this unit is located as my Haynes manual doesn't even mention it and the wiring diagrams totally ignore the air con system.

So for anyone out there with an odd air con operation, get the rad fan ecu checked out, it may save you getting very hot and bothered and wasting money on regases and compressor changes.

Just for info, my ebay VAG-COM and lead did not identify any fault codes at any time with the air con system. Seems like they are not worth bothering with, save your money for the real thing.

Cheers man, i was getting real paranoid about my Climatronic reading that! At least it is sorted now and does not cost the earth, there seem to be some well known problems with Climatronic but it is the first time i have heard that one.

I must admit I was highly dubious when the service manager called me to explain what they intended to do! That said, I had exhausted all of my ideas, so it seemed a logical path to try.

I have scoured this (and other VW) forums looking for possible answers to the problem, but no-one came up with that! Hence my reason for posting. Fortunately, the climatronic system seems to be behaving itself now - I don't want to think of the cost if the main control unit fails!

The joys of owning VAG - while they're running, they are lovely, it's when they stop that the bills start racking up! Bit like my old Lancia HPE, but that's another story.....

:beerchug:

Good to know about these hidden/undocumented 'features' and thanks for the write-up!

HI there,

I ve got a different problem ...my fans don t work and also the a/c don t think is working propery(i ve got a mk4 tdi with a/c not climatronic) meaning I turn it on and it s not getting as cool as it should be...now again I might need some gas inside but the weird thing is when i do output tests with vcds the radiator fan module does the job for a few seconds(the fans start to spin) and then stop but when the car is running none of the fans work ,not even with the a/c on or without.is the fans control module the one under the battery? I know that fans are a common problem on the mk4 but somehow it might be the same as yours...no a/c because fans don t work...

Any ideas?
Ths

Not sure about your problem being the same as mine, as mine wouldn't work with vcds on, even briefly! It is possible that you haven't enough gas charge to allow system to operate, or that the high or low pressure switches in the system (which prevent operation unless correct pressure is obtained) have failed.

My first task would be to have a reputable garage check the level of gas in the system (as this is easiest and cheapest) - should be between 720 and 790 grams (750 is usual). Any different and the system will not operate.

If all is well, then check compressor is working by putting 12v on the clutch connection with the engine running and a/c selected on, it should run briefly. If not, then it is signal from a/c control unit or fan module.

Hope you get it fixed soon.

The radiator fan control unit is bolted to a bracket on the left chassis leg under the battery and is not a common failure but failure of the large radiator fan is common. You can easily tell if the radiator fan/control is an issue with non-functioning A/C if it works when you are driving along but cuts out in traffic.