Things You'll Need
Screwdriver Philips or slotted
New AC unit circuit breaker
Testing a circuit breaker for proper operation that controls a central AC unit is the same process as with any circuit breaker. That safety device must be able to conduct electricity through the switch, as well as trip the unit out of the circuit when an unsafe condition occurs. By following a basic process you can perform this test without having to call in an electrician, and keep some money in your pocket during the procedure.
Remove all power from the circuit breaker that controls the central AC unit. This will generally be a two pole or 240 volt alternating current (VAC) circuit breaker. Switch the main breaker to the "off" position to remove all power to the panel box that holds the AC unit's circuit breaker.
Use the screwdriver, Philips or slotted, and remove the metal cover that protects the panel box. Keep the screws in a safe place so you do not lose them.
Remove the wires that are connected to the screw terminals on the circuit breaker in question and put the wires to the side.
Unlatch or remove the circuit breaker from the main bus bars of the panel box. Some breakers are directly screwed onto the main bus bars that conduct the electricity into the breaker. Other circuit breakers just "snap" into place.
Put the breaker on a flat surface and switch the breaker to the "on" position.
Turn the volt ohmmeter on and in the "Ohms" reading position. Touch the two bare probe ends together. The meter should read as Zero ohms or a shorted continuous circuit.
Place one of the probes to the screw end of the circuit breaker and the other probe to where the breaker connects to the bus bar. The ohmmeter should read zero ohms or a direct continuous circuit. This term can also be described as continuity.
Perform the test on the other side of the circuit. The results should be the same. If one or both of the circuit breakers switch show an open circuit, or infinite Ohms, with the switch in the "on" position the breaker is bad and should be replaced (see Resources below).
Test the circuit breaker in the "off" position. Switch the breaker to "off" and test both sides of the switch as in Step 7 above. The ohmmeter should read a full open or infinite Ohms condition. If the breaker shows any continuity, the breaker is bad and should be replaced.
Install the new circuit breaker for the AC unit into the panel box and reattach the power wires.
Reattach the cover to protect the bus bars and turn the main switch back to the "on" position.
Follow all state and local electrical codes whenever performing any type of electrical replacement or new device installation.