You can place your hand on the compressor and tell if it's running, as you should be able to feel the vibration (careful, it can get hot). Shortly (within a minute or so) after the machine is running, you should be able to see some frost building up on the coils around the evaporator. With the door open, all the coils won't frost up, but some will.
Changing the evap fan in these machines is a little tricky. The reason being Westinghouse used a two-piece motor, which is unique to their machines. The replacement motors out there today are only one-piece. The problem deals with the bracket required to hold the motor. Check out this link...
http://soda-machines.com/discussions/index.php/topic,7252.0.html.
This is a thread on the very same topic a few years back. I posted some photos in there on what I had to do to replace mine.