Volvo Repair: Air conditioning, ash tray, time brian

Question
Hi,  I checked the power at the silver canister and there was power there.  I had an assistant cycle the AC button on the dash and verified that the power at the canister turned on and off.  Can I conclude that the button switch is OK?  What do you recommend next?  Is there a wiring diagram for the system that I can get a look at online or email?  Thanks again for your help.
Brian (original question and answer below)


My wifes 1992 940 Turbo has a problem with the air conditioning. It seems like the compressor is not turning on. I have checked the fuse behind the ash tray and it looks fine and has continuity. With the engine running, fan on and AC button out I checked to see if there was any voltage at the wire leading to the compressor. I got a reading of .15v. I tried the same thing with the button in and got the same reading. She said it was working fine about a week ago. Is there a relay or some other fuse I can check. I dont think there is a leak in the system. I suspect it is just an electrical problem based on the fact that I am not seeing power at the compressor. Am I missing something? Is there something else I can check.

Thank you for your time.
Brian


Regis J Easler III Answers -
I would check power to the switch on the large silver canister near the firewall if no power to this then the most common thing I have seen is a problem in the conrtol panel.there is a solder joint inside the control panel that goes bad.you could try to remove the panel and look for the bad solder joint.  

Answer
with the switch connected there should be power out the other wire if the pressure in the system is good.you would also need to check the pressure in the system with a set of guages.if pressure is good and no power out of switch then switch is bad if pressure is low  then system is low on freon.