AC does not work but heater does

Back when I purchased the car the AC worked fantastic! We did a transmission swap due to a bad torque converter. When we got the car back the AC was no longer working. Just blowing hot air. We have tried to recharge the Freon, it is full and over pressurized. And we cannot bring it down. We think the AC pump might be out. But not sure. Just looking for more logical input.