Confident the run capacitor is bad.
Question is can a failed run capacitor destroy the motor windings?
I can peek in the motor housing and see mostly shiny copper windings.
120vac brush less motor has free bearings
This is an old Craftsman fan from the 1980's.
Last year, I oiled the bearings, and it worked great till a couple weeks ago, I no longer heard it running.

Motor is dead, no spin, no vibration, no nothing.
I verified it has 120vac power at the motor.

 

It is time for a new fan.

 

Or at least, a new-Motor.
It's probably a standard size and rating.
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An open capacitor is not necessarily bad, as a normal capacitor will read open-circuit with an ohmmeter.
Have you tried a new capacitor?

 

You can measure the resistance of the motor windings, the capacitor has probably dried out and gone open circuit.

 

Generally if the start/run cap has failed, the motor will 'Buzz', giving it a spin can often start it.
As per last post, check motor resistance, do the windings show any discoloring?

 

Have ordered a new capacitor. $7.50 to find out.
Pic is from when I first decided to use it, took it all apart and it was in great shape.

Capacitor is definitely open I think, top is also bulged up.
Ohmmeter reads infinity ohms, and reversing leads shows no meter change.
Motor is FASCO

 

If motor is still dead, will open it up and look.
With power to fan, I checked for volts across the disconnected capacitor wires and there was none.

Does that tell anything?

 

I tried charging cap with 9v battery, it does not charge up.

And don't these fan motors have a thermal fuse sitting on the windings?
I have gotten fan motors to run bypassing it,
If the cap failed, it could have caused motor windings to overheat and blown a thermal fuse, if it exists.

 

Motor winding burned and broke to the wires, so it's trashed. No fuse inside crappy motor.
I think the bad run cap caused it to overheat. So a bad run cap can destroy a good motor.
I have a fan furnace motor of 5.5" diameter. I can likely make it fit the clamp bracket used with attic fan.
Both are 1/2" shaft.
Old attic fan motor is 5" diameter and a 5mfd cap
Furnace motor, 5.5" diameter and says 7mfd cap
Ohmed out good, bearings good.
look good all around.
What if I use a 5mfd instead of a 7 mfd?
4 wires, multispeed motor, which speed would be best for an attic fan?




furnace blower motor 1/2 hp

 

And would the lower speed use less amps, motor says 8 amps?
wires for lower speeds have progressively higher ohms to white wire.
It is free though. And thermally protected, means has a fuse?
I feel like it is a good quality motor. Rotation is correct for fan blade.

 

You MAY get away with 5μf, but I would use on top speed if using just this value.

 

You MAY get away with 5μf, but I would use on top speed if using just this value.

Ok, I will get a 7.5mfd as no 7mfd are sold today that I see.
I did read you can go up in mfd and not good to go down.
If it works, lots cheaper than a new attic fan.
Since motor ohms out good, and bearings are tight, it should work is my thinking.

 

When used on a multi-speed inductive motor fan, the capacitor is a compromise in order to cover the multi-used phase shifts that occur on each speed.
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Don't be so hard on the Motor and Capacitor manufacturers,
that Fan may be running in Air that is around ~150F ( 65C ) for long periods.

You should at least make sure that the Capacitor that You get is rated for those Temps, or higher.
If You can't find a Capacitor rated for that kind of Heat,
then get one that is at least rated for twice as much Voltage.
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BTW, Personally I do not use motor capacitors that originate from China, they have a very poor history.
You can't go wrong with something like CDE, oil filled paper types, intended for this purpose.

 

I found a capacitor 7.5 mfd that was in an extra air handler.
It is quite long compared to the 5.
Tested motor and it runs good.

And I expanded the mount bracket to fit 5.5 " motor.
Here it is mocked up.
Looks like everything will fit with new drilled holes.

Will need new bolts and nuts and washers. OEM welded nuts to sheet metal.
I will drill new holes and use threaded rod to hold rod to sheet metal, like nut washer sheet metal sandwich.
The 2 piece rubber bushings will slide on the rod, fan bracket will slide on and outer bushings with washer and nut.

I may even have 1/4 threaded rod here, then just need nuts and washers.

will mount with oil plugs up

 

This fan is a gable end mount.
I wonder if run caps can actually get higher temp ones?
This one is good to 158 *F, has large amount good feedback.
BOJACK 7.5 uF ±6% 7.5 MFD 370V/440V CBB65 Oval Run Start Capacitor for AC Motor Run or Fan Start and Cool or Heat Pump Air Conditione: Amazon.com: Industrial & Scientific

• BOJACK 7.5 uf MFD 370V/440VAC Oval Run Start Capacitor
• Operating Temperature Range -40 ℃ to +70 ℃/ -104℉ to +158℉
• This Capacitor Will Run Compressor And Fan Motor
• UL Recognized,Engineered For Safety 10 000 AFC Anti Explosion Pressure Switch
• Replacement for :27L566BZ3 , 27L566 , 27L566S , 97F9001 , Z97F9001 ,97F9001BX ,CPT-00120 ,TP-CAP-7.5/440,TOCF7.5

 

My experience is that a capacitor with not enough capacitance will not allow a motor start, but it might run with a spin start. That was on a SEARS furnace my dad bought 60 years ago. So a bunch of 0.47 Mfd caps across the 5 mic cap and the motor ran like that for many years. So adequate run cap is mandatory for the motor to run. Even a motor with multiple taps for different speeds.

 

CDE previously quoted, 370v AC ±10%.
Motor run rated !
Oil filled Paper.
Too high a capacitance same result as too low.