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.

I can't answer your question, but just in case you have not researched this much, you are fighting something that many, many owners of 91, 92 and the native R134a 93 240 owners have fought before, and the consensus is... wire it to come on with the compressor or the AC switch, because the pressure either never makes it up there or the switches just can't last.

Without much personal investigation of this, I just "blew it off" as another early 90's emergency ECN stimulated by the Montreal protocol. ECN is shorthand for engineering change notice which is doublespeak for "emergency fix."

Who is going to go sit in traffic and hook up a high side gauge to see the pressure crest the spec for the HP switch? Couple beers on a slow day in July maybe?

Also a matter of consensus: that fan helps a lot. Sure it is noisy.
--
Art Benstein near Baltimore

Married men live longer than single men do, but married men are a lot more willing to die...