How to Test a Vacuum Capacitor

Unplug the power cord for the electronic device containing the vacuum capacitor.

Remove the cover on the device containing the capacitor by taking out the screws with a screwdriver. The capacitor inside is cylindrical, typically made of tempered glass, and contains a series of small steel baffles inside.

Grip the capacitor at its widest point and pull straight up to disengage the two wire terminals from the sockets underneath.

Connect the negative terminal of the adjustable power supply to the multimeter's negative test probe, which is typically black. Clip the power supply's positive terminal to the positive wire on the capacitor and attach the multimeter's positive, or red, probe to the positive wire on the capacitor.

Plug in the adjustable power supply to an electrical outlet. Set the multimeter to test for voltage.

Dial the control knob on the adjustable power supply clockwise to increase voltage gradually. Raise the voltage to the rating on the capacitor within one minute, turning the knob on the power supply slowly. If the light in the capacitor glows steadily after one minute and continues to hold steady with voltage supplied at the components capacity, then the part is operating normally. If the light flutters or goes out after one minute, replace the capacitor.