There are many types of contactors. For example: a single pole, a double pole or a triple pole. All contactors are rated by amps. A contactor works when power from a 24V transformer activates a coil (magnet) in the bottom of the contactor and it pulls the contacts down. You will find contactors used a lot in air conditioning equipment and some electric furnaces. To test your contactor, you want to check for continuity (to see whether or not you have a complete circuit). By using a voltage meter, you are able to test whether or not your contactors circuit is complete. If your meter beeps when both ends are touching, you know that you have a complete circuit.