S60 Air Con: Strange behaviours with regards to the aircon..

[cjard]

My S60's aircon isn't as good as when I bought it - it was going cool, but not as cold as before. I had the system recharged yesterday and the guys who did it noted that it would go cold, then warm again. While using the Volvo to drop our other car off at a different garage, the Volvo had been parked up idling for a few minutes when there was a loud groaning noise from the engine bay. I popped the bonnet and noted that when the air con clutch was engaged there was a noise a bit like a vuvuzela - I got a video of it: http://youtu.be/J03IctDnL18

the guys in the garage stuck their diagnostic machine on the high port and noted that it was reading 20 bar after the engine being off for 15 minutes. they did a recovery (recovered 1150g gas which I understand is higher than default) and decided to test by putting back slightly less than spec (900) in case there was a blockage somewhere.
Starting the engine up (cabin setting on max cold) and watching the pressure, the compressor kicked in and the high pressure reading just climbed and climbed..at around 30 bar I shut the engine off as I wasn't keen for an explosion
They noted that the cooling fan on the rad didn't fire up at any time and couldn't find another fan so they currently think something is wrong/preventing the fan from firing up and cooling the gas, which I'm given to understand would have reduced the pressure.. I've not tested it extensively, but it might be true that the aircon blows cooler when the car is moving then when standing in traffic

So my questions at this point -
Should the radiator fan have activated, or do these cars cool the compressed gas another way?
What's the maximum pressure on the high side/what pressure is it supposed to run at?
Was the humming from the compressor possibly a sign of excess pressure build-up?
Is there supposed to be a pressure sensor that deactivates the compressor over a certain pressure (and if so, what)?
What are my next steps for troubleshooting my air con?

Thanks guys

[jim annandale]

You definately need the cooling fan at idle, the pressure will increase without it, it will probably be the air con pressure switch, not sure where you will find it but usually on the dryer (not sure where that is either as I've never looked). It could be the cooling fan itself, could you not give it power and see if you can make it run. I'm a bit bed ridden at the moment and can't really climb under the bonnet and look round without causing myself more injury. Some one on here will find the a/c press' switch and how to run the fan. The a/c would work while you are moving but the pressure will rise as soon as you stop in traffic.

[cjard]

thanks jim. I'll get the multimeter out
I'm fortunate enough to have a friend with two s60s the same age, so I'll nip round to his and observe the behaviour of his cars, don't go crawling around under yours..