Non working A/C or phantom supercharger?

Quick question before I take my truck into the shop tomorrow. Last year my truck sat for several months at a time. When I got back my AC was blowing warm air and when the AC (and defrost) was engaged it sounded like my truck had a whiny supercharger. I'm taking my truck in tomorrow to get it's AC serviced but what could be the cause of this? want to prepare myself a bit...
thanks in advance.

 

If your truck just sits for long periods of time maybe your belts are worn out/weathered prematurely.

 

Belt may just be dry from sitting a while. You could spray some lube on them, but I'd personally just change the belt. It's pretty easy to do yourself and is cheap.

 

I'll take a look a the belts. The big issue is the AC does not blow cold. The truck is driven daily but on some shows (I work in TV) I will have a rental for prolonged periods of time.