Jump to content
Sign in to follow this  
John Dirks Jr

heat pump question

Recommended Posts

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
tn_201171543046_P1150559.jpg

29.58 KB

Click to Enlarge
tn_201171543115_P1150578.jpg

33.83 KB

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

If it had an open winding the motor wouldn't heat up. He was clocking 173 degrees.

Oops, I meant 'open start winding'.

Marc

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

The accumulator didnt look too good. What do you think?

Click to Enlarge
tn_201171521936_P1150583.jpg

26.55 KB

That's just the plastic encapsulation you're looking at. I wouldn't worry about it.

Marc

Share this post


Link to post
Share on other sites

The accumulator didnt look too good. What do you think?

Click to Enlarge
tn_201171521936_P1150583.jpg

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

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...