Fan making humming sound but not turning - CBB61?

[Cirkit]

I am trying to repair an air filter. The fan just makes a humming sound on any of the three speed settings but does not rotate.

I've measured the 1.5µF motor capacitor (CBB61) and it's around 1.2µF. The tolerance of the capacitor is 5%. Would this be enough to prevent the motor from rotating?

Even if I spin the fan and power on the air filter, the fan still does not rotate.

Could I temporarily add a 470nF Class-X capacitor in parallel with the CBB61 to prove if it is the reduction in capacitance that is preventing the fan from rotating?

 

[Minder]

Sounds like a PSC motor if so and the cap is defective, it would normally spin up by giving it a spin when powering up.
Measure the two windings, they normally would be equal resistance,
If replacing the cap, it requires a AC motor run rated version.
M.

 

[Cirkit]

Thanks for your reply Minder.

I measured resistances between the 4 colours on the 4-pole connector and also between both capacitor connections to each of the 4 wires (with the capacitor removed):

4-pole connector
Green - Black 458Ω
Green - Red 126Ω
Green - Yellow 297Ω
Black - Red 332Ω
Black - Yellow 161Ω
Red - Yellow 172Ω

Capacitor connections (Grey & White)
Grey - Green 215Ω
Grey - Black 672Ω
Grey - Red 341Ω
Grey - Yellow 512Ω

White - Green 458Ω
White - Black 0Ω
White - Red 332Ω
White - Yellow 160Ω

I'm guessing the configuration is something like this for the three speeds:

 

[Minder]

That would be the typical hook-up.
I overlooked the 3 spd.
M.

 

[73's de Edd]

Your readings certainly correlate with 215Ω 's as being the auxillary winding resistance.
If only having that .47 poly X type cap, I would certainly venture shunting it across the run cap and then putting the unit in HIGH speed and giving the fan / impeller / shaft a spin in the CORRECT direction.
If still just a HUMMMMMMMMM, pull / disconnect the original capacitor out from circuit and then just SOLELY use the sub capacitor and go thru the same procedure again.

 

[Bluejets]

Bearings tight perhaps?
Not much torque in these motors.

 

[Cirkit]

Your readings certainly correlate with 215Ω 's as being the auxillary winding resistance.
If only having that .47 poly X type cap, I would certainly venture shunting it across the run cap and then putting the unit in HIGH speed and giving the fan / impeller / shaft a spin in the CORRECT direction.
If still just a HUMMMMMMMMM, pull / disconnect the original capacitor out from circuit and then just SOLELY use the sub capacitor and go thru the same procedure again.

Thanks for the suggestion. I temporarily replaced the motor run capacitor with a Class-X2 one that I had of slightly higher capacitance and the fan worked!

The one on the left is the original capacitor and the one on the right the X2 temporary one I tested:



So what is the difference between a run capacitor and X2 capacitor?

 

[Bluejets]

x2 is a mains rated capacitor, can withstand high voltage peaks.(2.5kV)

 

[Minder]

AKA Metallized polypropylene material, high insulation and suitable in withstanding over-voltage stress etc.
M.