first check and make sure there are no blown fuses. Second, turn the car to acc. unplug the a/c plug from the compressor and turn the a/c on. Check with a volt meter to see if you're getting power to your compressor. Your a/c harness should be part of the body harness and should not matter that a new motor was put into the car. I'm guessing a fuse if the a/c light doesn't come on.. keep us posted.

-Mike