Dual Capacitors On Heat Pump

[hockeyoligist2]

Two months ago I replaced the condenser fan motor on a heat pump, bearings had gone bad. The new motor from WW Grainger (cross referenced as a replacement motor) has stopped working. I can spin it and it runs. The Dual capacitor checks good and I also tried a capacitor from Grainger listed for the motor. I am not familiar with dual capacitors (and capacitor run motors in general since most everything I work with is 480-up) and I'm wondering if this could have caused the failure? The replacement motor will be in tomorrow and I don't want to let the smoke out of the new one!

 

[LarryFine]

A 2-cap motor uses one cap for the start winding and one for running. The start cap and its associated winding improves starting torque; the run cap improves running torque.

The start cap is usually switched out of the circuit by a centrifugally-operated switch. Its contacts may be burned. Since you're replacing it, that point is moot.

If the new motor does not come with caps, I strongly recommend installing new caps. Between their cost and the labor to return again, it's not worth it to do otherwise.


Added: Capacitors in series with part of the windings introduce a phase shift that creates a rotating magnetic field, mimicing a poly-phase supply.

 

[hockeyoligist2]

The cap runs the fan and the compressor. The fan motor is this one:

http://www.grainger.com/Grainger/items/4M226


Condenser Fan Motor, Permanent Split Capacitor, Totally Enclosed Air-Over, 1/4 HP, Number of Speeds 1, Nameplate RPM 825, NEMA/IEC Frame 48YZ, Voltage 208-230, 60 Hz, Full Load Amps 1.8-1.7, Stud Mounting, Auto Thermal Protection, Insulation Class B, Service Factor 1.00, Sleeve Bearings, Ambient 60 C, CW/CCW Rotation, Length Less Shaft 5 In, Shaft Dia 1/2 In, Shaft Length 6 In, Body Dia 5 5/8 In

 

[LarryFine]

Ah, a dual cap. All that is is two caps in a single case. "Permanent split" means that the cap is a run cap, not a start cap. It does, of course, aid in starting, too.

My advice is still the same: replace the cap when you replace the motor.