Why did the air conditioning quit working on my car?

it is a 1998 Ford Taurus 4 door, got almost 199,000 miles on it. Drives everyday. New ac kit installed 4 months ago.........ac clutch not kicking on. I think it is an electrical problem. I triggered the pressure line valve to make sure freon was in the line and has good pressure and full of freon. I checked wiring to compressor with tester, had no hot, so i ran a jumper to battery to compressor, it came on, worked fine, blew cold air inside. removed jumper wire......could it be a relay? where and which one? under hood box has 3 big black relays, 3 small white relays, several small fuses, they all looked fine, none appeared blown so far