Air con compressor clutch

[ayatollah]

I have a 2000 TDi 110 and last week the aircon stopped working. I presumed it needed recharging and this morning took it to have it done but was told by the mechanic there that it was full of gas and he thought it was the clutch on the compressor not engaging.
I found this wonderful forum whilst doing a search on compressor clutches for seats.
One thread describes tha clutch coming completely off and the aircon then making a metallic noise. Mine doesn't make any noise - just no cold air. I also found a thread on diagnostic codes and found these on it :
18064 p1656 A/c clutch relay circuit short to ground and
18065 a/c clutch relay circuit short to bt.
Can any kind soul tell me if these relays could be causing the problem and if so where they are and
Whereabouts in the engine bay is the clutch for the compressor (and is it possible to take it off, clean it up and refit it without discharging/recharging the system)?
Thanks
David

 

[Muttley]

The compressor is driven by the multi-v belt, the one that you can see at the lefthand side of the engine. It also drives the alternator and the power steering pump. The aircon compressor is the lowest of the three and will be difficult to see. It has large-diameter refrigerant pipes coming from it.

The clutch is part of the pulley and is a magnetic device, as the pulley is spinning all the time the engine is running but the compressor has to be switched on and off. To engage the clutch, current is passed through an electromagnet which draws the clutch parts together and drives the compressor.

It is possible to remove the pulley and clutch without disturbing the refrigerant circuit.

Here is a general article on car airconditioning, describes the compressor and the clutch.

http://www.musclecarclub.com/library/tech/air-conditioning.shtml

No idea where the relay is, I'm afraid. The wiring diagrams I've seen show the clutch being controlled by the radiator fan control module, wherever that is.

 

[ayatollah]

Thanks for that Mutley.
I'd like to rule out other things before getting new compressor/clutch. Possibilities (discovered on this site) are
broken relays
broken wire in the air con control unit (wherever that is)
broken temperature sensor (either in passenger wing mirror or wiper blade?)
I was quoted 600 euro + fitting for a new compressor clutch - hence wishing to eliminate the other things first.

David

 

[Muttley]

ayatollah wrote

Thanks for that Mutley.
I'd like to rule out other things before getting new compressor/clutch. Possibilities (discovered on this site) are

broken relays

I can't find any relays in the circuit diagrams. The radiator fan control unit (which I think is underneath the battery , at the right front of the engine compartment) seems to switch the clutch power directly.

broken wire in the air con control unit (wherever that is)

The Climatronic control unit is integrated with the display and control panel in the center console, underneath the radio head unit.

broken temperature sensor (either in passenger wing mirror or wiper blade?)

The outside air temperature sensor on the Toledo is in the front bumper. It is the little pip mounted in the black part of the bumper, underneath and to the left of the nearside foglight. Not sure how much one is, but it may be possible to test by replacement using a known good sensor.

There is another sensor in the fresh air intake duct.

There are other temperature sensors, for inside temperature, in the headlining, dash and footwell. Also a photosensor in the defrost vent under the middle of the windscreen, measuring sunlight coming into the car.

I was quoted 600 euro + fitting for a new compressor clutch - hence wishing to eliminate the other things first.

Well, it should be easy enough to test whether the clutch is engaging. The compressor is a significant load on the engine and will cause the revs to drop when it engages. Set the Climatronic to "LO" (which will call for continuous cooling) then use the snowflake button to switch the compressor on and off.

 

[ayatollah]

Clutch definitely not engaging. Just have to bite the bullet and leave it to a dealer. Thanks for the help.
David