I finished resurrecting my A/C a few hundred miles ago, and it works well. However, I've noticed the auxiliary fan never turns on. I'v verified the fan and the relay work by inserting a jumper in the pressure monitor switch contacts. This is the switch behind the passenger side headlight near the lower radiator hose, connected to the A/C line. The part number is 3540657.

I know I can just ground the fan and have it run when ever the A/C switch is turned on, but that's over kill. And since I've put a lot of effort in repairing the system, i'd like to get this last part working.

A few questions:

- how do I test the operation of that switch?

- if it's failed, can I replace it without compromising the A/C charge, or does it need to be evacuated first?

- I know these switches are hard to find, but Tasca seems to have them: http://www.tascaparts.com/oe-volvo/3540657. If they don't, any other suppliers I could try?

Thanks for any help or suggestions.