Drove to the store two days ago, AC blowing cold. Got back in car (2007 Town Car), blowing hot air. Compressor will not come on at all now. Replaced AC Relay and low pressure switches. 15amp feed fuse is good. When first turning on the AC it sounds like the compressor kicks on, but it's really just the relay (or something) trying to get it going. Maybe it is the compressor, and the clutch is just locked. Can I bang on it with a hammer? Or do I need to replace the clutch?