Run caps stay in the circuit and are rated in microfarads, often a dual cap serving both compressor and fan, such as 45 and 5 MFD, typically within plus or minus 6 percent. Start caps give a brief boost and drop out. A weak or failed cap is one of the most common no-cool calls: the motor hums, overheats or won't start. A bulged top is a sure giveaway, but techs test with a meter rather than trusting looks.
Fan's not spinning and the compressor's tripping on overload, cap reads 28 on the 45 side, there's your problem.
Discharge a cap with an insulated resistor before handling it; a big one can bite long after the power is off.
Also heard as
- capacitor
Related terms
Contactor
A heavy-duty relay that uses a 24 volt control signal to switch line voltage to a compressor and condenser fan.
Hard start kit
An add-on start capacitor and relay that gives a struggling compressor extra torque to start.
LRA
Locked rotor amps: the current a motor draws at the instant of starting, before it turns, listed on the nameplate.
Head pressure
The compressor discharge or condensing pressure of a refrigeration system.