Climate Control Problems?

I have a 1989 Lincoln Town Car I purchased new Septmenber 1989. It has a 5.0 engine. I'm trying to keep it in good shape. Recently I turned on the AC only to have hot air come out of the vents. The temp control is as cold as it will go. It blows "screaming hot air" on every selection. The vents, mix and defrost have the same result. The AC compressor runs when I turn on the AC or defrost and HOT air comes out even when the temp control is set to the coldest seting. I noticed the problem after I had the water pump replaced. Would there be any vacuum line near the water pump the mechanic may have knocked loose? Seems like a vacuum problem somewhere. Can you help me try to fix this myself? Thanks, Bob.