The A/C in my escort doesn't work, I took it to a shop to have them check and my Freon is full. When I hit the A/C switch when it was working, the engine rpm would drop a little bit so I'm thinking that the compressor clutch isn't engaging. I got a used compressor, but I'm wondering what would be the best order to check for things wrong before I go to replace the compressor. Can anyone help me? :?