HVACPROTECH® TECHNICAL ARCHIVES

~ Capacitors are rated by microfarads (uf) and voltage. The rated capacitor uf should not be changed, since the
motor operates at maximum efficiency when using a specified capacitor size. Although a plus or minus 10 %
rule of thumb applies to the microfarad rating when changing out a capacitor it is not recommended.

~ If necessary, the replacement capacitor voltage rating can be higher than specified, but not lower without
effecting the capacitor life. The specified voltage is a limit, not a rating. Back EMF produced by a motor in
operation, should not exceed the capacitors voltage rating. You can replace a 5/370 with a 5/440, but not in reverse.

~ Always replace the run capacitor when installing a new motor. If a defective capacitor is in the circuit the
motor will probably not run. If it does run, it will operate as if it is overloaded. The motor speed will be low; it
will overheat and probably activate the motor overload protector causing short cycling.

~ Capacitors can hold a charge for long periods of time. To prevent shock the capacitor should be discharged
before it is removed. The proper procedure to do this is to use a 5000 to 20000 Ohm bleed resistor.
However, the primary reason for bleed resistors on a start capacitor is to prevent the discharge of this energy
back through the potential relay contact points. This condition can create arching which leads to sticking points,
and ultimately, a blown start capacitor, and worse yet, a failed compressor.

~ When replacing a faulty start capacitor, always replace the potential relay. It is most likely the relay caused
the Capacitor to fail. It is always good practice to replace all start and run components when installing a replacement compressor.

~ You will have capacitors for the Start Winding only in normal A/C applications. It is confusing because we
call them Start and Run Capacitors, and we have Start and Run windings. All Run capacitors go to the Start
winding as do all Start capacitors. In actuality, we have a Common tap, a Main winding, and a Motor winding in all PSC motors.
Three terminals, Two windings.
Main-----C----Motor
Run------C-----Start