I've got a similar problem with my V90 that is 1000 miles away at college. My parts guy says there are three switches around the compressor. One has a three prong plug, the others have two prong plugs. I ordered all three ($25, $25, and $80). My other advisor, Mr. Murphy :), told me it would be the most expensive unit that is broken. The parts guy confirmed that is what they sell the most of--and his computer says it functions both to control the cooling fan and some high pressure function.

So, how do I direct my daughter to pull and plug the right switch? I guess the 3-prong is a little larger than the others, but the parts guy says they are very similar. Moreover, since Volvo changes their parts numbers, the new ones may not match the old.