Potential relays are wired to all three compressor terminals and not just to the compressor run and start terminals.
When a compressor motor fails to operate and the potential relay is suspected to be the cause, the best way to test it is to use a compressor test cord. (See fig. 35,36) Start the compressor by bypassing the relay. If the compressor starts running, the starting relay must be replaced. (Potential relay testers may be obtained from major refrigeration supply dealers if that method is preferred. They all come with complete instructions.)