John Dirks Jr Posted July 15, 2011 Report Share Posted July 15, 2011 I had a heat pump (in cool mode) of the upper floor fail to respond to the Tstat controls yeaterday. I noticed that the motor for the fan had gotten really hot. I figured that maybe the motor was seized so I poked my screwdriver through the grill to see if the fan would spin and it spun freely. So, I assume the motor was not seized since the fan spun free. Anyway, what would cause the motor to heat up like that but the fan not spin? Click to Enlarge 29.58 KB Click to Enlarge 33.83 KB Quote Link to comment Share on other sites More sharing options...
Chad Fabry Posted July 15, 2011 Report Share Posted July 15, 2011 Bad start capacitor. Quote Link to comment Share on other sites More sharing options...
Terence McCann Posted July 15, 2011 Report Share Posted July 15, 2011 Bad capacitor. Chad squeaked in just in front of me. Actually though I would think it's a run cap. Those motors typically don't have a start cap. Quote Link to comment Share on other sites More sharing options...
Marc Posted July 15, 2011 Report Share Posted July 15, 2011 I'd finish the diagnosis by giving the fan blade a spin with the power on. If it comes up to speed, it's just the capacitor. If it doesn't, open winding in the stator. If it speeds up but not as fast as it should, shorted start windings and perhaps a bad capacitor too. All this assumes that the bushings are good and have not too much friction in them. BTY, the capacitor should always be replaced with a new motor. Marc Quote Link to comment Share on other sites More sharing options...
Terence McCann Posted July 15, 2011 Report Share Posted July 15, 2011 If it had an open winding the motor wouldn't heat up. He was clocking 173 degrees. Quote Link to comment Share on other sites More sharing options...
Marc Posted July 15, 2011 Report Share Posted July 15, 2011 If it had an open winding the motor wouldn't heat up. He was clocking 173 degrees. Oops, I meant 'open start winding'. Marc Quote Link to comment Share on other sites More sharing options...
John Kogel Posted July 15, 2011 Report Share Posted July 15, 2011 Actually what causes the heat to build up is friction. The resistance in the windings working against the magnets. But this friction is due to what you smart guys said, failure of the start circuitry. Quote Link to comment Share on other sites More sharing options...
Marc Posted July 15, 2011 Report Share Posted July 15, 2011 Actually what causes the heat to build up is friction. The resistance in the windings working against the magnets. But this friction is due to what you smart guys said, failure of the start circuitry. Friction is a mechanical term but your analogy is on the spot. The heat in this case would be the resistive losses that result from the high currents flowing through the windings. This current would be at the same magnitude as the starting current of the motor which, for a capacitor start induction motor, might be twice or three times the rated maximum load current specified on the motor nameplate. That's right, these motors will burn themselves out in time if power is applied and the rotor isn't up to speed. Within the rotor on John's stalled motor are eddy current losses in the squirrel cage windings and hysteresis losses in the magnetic core. These losses all manifest themselves in the form of heat whenever the rotor isn't up to speed. Marc Quote Link to comment Share on other sites More sharing options...
John Dirks Jr Posted July 15, 2011 Author Report Share Posted July 15, 2011 I bumped the fan with the power on and it didn't get up to speed. It didn't get any speed for that matter. I've had units with bad capacitors before. Usually they have a slight buzzing sound of the unit trying to start up. This one was dead silent with a heated fan motor. BTW, doesn't the capacitor serve the compressor motor and not the fan motor? Quote Link to comment Share on other sites More sharing options...
John Dirks Jr Posted July 16, 2011 Author Report Share Posted July 16, 2011 The accumulator didnt look too good. What do you think? Click to Enlarge 26.55 KB Quote Link to comment Share on other sites More sharing options...
Terence McCann Posted July 16, 2011 Report Share Posted July 16, 2011 BTW, doesn't the capacitor serve the compressor motor and not the fan motor? No, it is possible to have more than one cap ie a/c systems. Quote Link to comment Share on other sites More sharing options...
Marc Posted July 16, 2011 Report Share Posted July 16, 2011 The accumulator didnt look too good. What do you think? Click to Enlarge 26.55 KB That's just the plastic encapsulation you're looking at. I wouldn't worry about it. Marc Quote Link to comment Share on other sites More sharing options...
plummen Posted August 25, 2011 Report Share Posted August 25, 2011 The accumulator didnt look too good. What do you think? Click to Enlarge 26.55 KB That's just the plastic encapsulation you're looking at. I wouldn't worry about it. Marc Most newer systems(last 20 yrs anyway)have a split cap for both the compressor and fan,Some units have a pressure switch that controls the fan coming on and off Quote Link to comment Share on other sites More sharing options...
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