Motor & Start Capacitor Diagnostics

[richie00boy]

Our cooker hood fan has stopped working. It's a 3 speed fan. The control panel works and the 3 relays for each speed click as expected.

I thought it might be the start capacitor, but testing that it doesn't read short and seems to charge up and discharge (only tested with basic digital multi meter). So now I'm wondering if it could be the centrifugal switch in the motor. This circuit is reading 158 ohms, could be indicative of a failing (closed) switch or is it just a winding resistance I'm measuring?

Image below is the wiring diagram.

 

[brightspark]

shell out and buy a new one . not worth fixing

 

[richie00boy]

Its not a cheap hood. If its a 50 quid motor to fix its worth it.

 

[piman]

Hello Richie,

I would doubyt that there is a capacitor switch in such a motor. Have you checked that it is free? If so switch on and spin the motor, if it runs then it's a capacitor problem. Any symptoms before it stopped working?

Alec

 

[richie00boy]

The motor spins freely and if you turn the unit on or select any speed there is no attempt whatsoever from the motor and if I spin it to help still nothing.

Is it only with start and run caps that there is a centrifugal switch then?

The hood was working fine then one morning stopped extracting. Its about 2.5 years old, just 6 months out of warranty

 

[piman]

Hello Richie,

modern single phase motors tend to have the capacitor permanently in circuit. Your next check, if you haven't already is to check for supply at the motor. Don't forget that the neutral needs to be sound (which your drawing doesn't seem to show, unless the speeds are switched via the neutral ?).

Alec

 

[carbon]

Is there voltage at the control panel outlets

 

[richie00boy]

I'm going to check the voltage at the speed outputs. Just been doing what I can without cutting too many wires so far.
Piman, neutral is shown.
Why do you think there is no centrifugal switch?

 

[carbon]

As piman has already suggested a lot of single phase motors have permanent run caps so no need for a centrifugal switch. Would have thought max speed may be in the 2800 rpm range with possibly a 4uf cap

 

[brightspark]

I'm going to check the voltage at the speed outputs. Just been doing what I can without cutting too many wires so far.
Piman, neutral is shown.
Why do you think there is no centrifugal switch?

because there never is in cooker hoods

 

[piman]

Hello Richie,

there are four wires shown on your diagram, excepting the capacitor, one brown to live and three to the three speeds. It could be that they eventually go back to neutral but that's not clear?

P.S., there is something wrong with your diagram as the plug is opposite polarity than the input to the controller?

 

[richie00boy]

I was assuming that the speed lines were neutrals. The tracking back is probably on the PCB.

 

[richie00boy]

After holidays and other stuff got time to look again today. Think its the motor dead as I wired speed 1 and live direct to mains and it made absolutely no attempt. Tried giving a helping push but nothing still.

 

[brightspark]

wasting your time

 

[angellonewolf]

get a new one £85 fromwhat i seen in the last few months when looking for kitchen stuff the differance in cooker hoods in very small even from the £85 to £300 the noise they make and volume they move all seam to be adverage just look for the one for a small or medium kitchen with the lower noise output 56 to 66 is about adverage my hood moves 430lpm for noise 56db aprox and still sounds like there is a jet engine in the kitchen

 

[richie00boy]

Thanks but its a high performance (almost double that flow rate) and fairly expensive one so looking to repair.

 

[angellonewolf]

is there a make on the motor ?

 

[richie00boy]

The motor is buried in plastic housing. Will see if I can get it out but busy over next few days.

 

[carbon]

Have you checked that the capacitor hasn't failed

 

[dobbslc]

I had a cooker hood that had a thin blue strip of light at the front edge of it when the main lights were tuned on and one day it wasn't working so thinking it would be only a few quid I looked it up on the Rangemaster website. £400!!!!!
Ffff what?
Anyway it turned out to be an electroluminescent strip recessed into a clear plastic strip and it had burnt out.
I'm not paying £400 for a poxy light I thought!
I found an electroluminescent strip kit on fleabay for £10 but it was 3mm too wide (the Rangemaster one's seem to be a special size) so I had to mill the recess in the plastic strip out on my mill. Fitted a new strip and soldered the wires to the existing controller and it works!
Result.