Air con problem

[farside]

The aircon on my 03 Octy TDi has stopped working, now when AUTO is selected on the Climatronic there is no cold air, just air at ambient temp. The clutch does not engage on the compressor, it remains static at all times. I can turn it by hand when engine is stopped, it appears to turn freely and smoothly. Presumably when the clutch engages you can see it spinning at pulley speed?

I checked the 2 wires on the compressor (green and brown). Using a multimeter i think brown is earth, and there is continuity so earth is ok, and green is 12V. So it appears the compressor is getting 12v ok. The strange thing is that 12v is always present - ignition off or on, climatronic set to econ or auto. I bought a Haynes manual hoping for a circuit diagram for aircon, but it is not included (?!"?) The aircon fuse F16 is ok. So I am a bit stumped without a diagram.

So, i borrowed a vag.com connector and shareware, and got a fault code on the HVAC module - 00792 A/C pressure switch F129. There may be other codes but this shareware version does not divulge them.

I think the pressure switch is on the bulkhead, slightly to right of centre on my car, attached to aircon pipe? Is there any way of testing this switch?

Any suggestions ? Thanks in advance.

[Dilbert]

Out of gas? If its not used regularly all year around, the seals supposedly dry up and the gas leaks out. First thing I'd check anyway - in some systems (not sure about the Skoda) you'll find two nipples for charging the gas. A tiny press on one with a suitable implement and you'll hear if gas is being released. On another car I've seen an almost empty system characterised by a small hiss then nothing. That's my guess anyway.

[Tech1e]

It will be 12v all the time, IIRC the earth is switched to turn the compressor on. An easy way to check if the clutch is engaging is to pull the plug off and give is a 12v and earth, it then should click in and out.

But you will get a pressure switch fault if there is no gas, this will stop the compressor cutting it.

[farside]

Yeah out of gas is a good guess! My friendly building maintenance engineer at work put his aircon gauges on it and no pressure there, so he injected a little refrigerant and now it works. Could not find any trace of a leak with his electronic sniffer.

I reckon there may be a leak so i will wait to see it this cures it or not. I have been using the aircon about once a week through the winter to keep the seals good. If it leaks again then it's time for a visit to my local aircon specialist to find the leak.