Run Capacitors for HVACR

Run Capacitors


Almost all run capacitors use oil and paper as the dielectrics. Because of the hazards involved with oil, a system of protection was devised to prevent fires from occurring within the equipment. The figure on the right shows how a fusing device is incorporated into the capacitor. This safety feature is designed to prevent an explosion or fire that could result from a shorted capacitor, but it can also create a service problem if the capacitor is not discharged correctly.



A capacitor can hold a charge for several days (depending on its size and capacitance value). The old “tried and true” method of discharging a capacitor was to use a screwdriver or jumper wire to short across the  capacitor’s terminals. If you were to place a direct short across the terminals, you could possibly destroy a good capacitor. To prevent this, capacitor manufacturers recommend that a bleeder resistor be used as a discharging device. A 15,000-Ω, 2-W (brown, green, orange) resistor with jumper clips is the easiest and safest way to discharge a capacitor. If you are in doubt about whether a capacitor is charged or not, simply bridge the capacitor with the resistor.

EXCERPT FROM ELECTRICITY FOR HVACR TECHNICIANS available from the online store at RSES (Refrigeration Service Engineers Society) The HVACR Training Authority

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