Attic fan motor problem

[evsisson]

My relatively new two-speed attic fan does not start when the switch is moved from "off" to the "low" position. However, it will start if moved from "off" to the "high" positon. I can operate the fan on "low, by first starting it in the "high" position, then moving the switch to "off," and then, before it stops turning, moving the switch to the "low" position. I check the switch's continuity, and it seems to be OK.

1. Is this behavior indicative of a known motor problem?

2. Can the condition be fixed?

3. Is it dangerous to continue operating the fan this way?

[joed]

It's dangerous only if some one turns it to low without going to HI first and the motor doesn't start it could overheat.

[Wgoodrich]

Did you use a speed control switch that is listed by UL for the purpose? Most speed switches I know of if not all are designed when listed for hte purpose to turn on with high position then turned down to desired speed.

Did you make your own speed control or use a lighting dimmer as a speed control?

Wg

[evsisson]

The switch was installed by an electrician, but it seems pretty cheap. It's plastic and has a three position rocker switch, the center position being "Off," so I pass thru the "Off" on the way from "High" to "Low." I forgot to mention before that it worked fine for a couple of years before this happened. Maybe I should just buy a new switch to see if that fixes it.

[joed]

If it worked fine it is more likely a problem with the motor. If it has bushings and not ball bearings the bushing could be worn or gummed up. Maybe the motor only needs a bit oil.

[Wgoodrich]

I am suspecting that this switch is for a smaller motor and not listed for the motor it is connected to as a controller. I suspect the switch is not designed to be used in this manner for that motor. If this is the case then the fan may be damaged or the switch may be damaged. Also may be a simple as a loose connection.

Just my opinion

Wg

[Tesseract]

I have seen motors used for this purpose that actually had separate windings for high and low. That switch isn't necessarily a speed control at all, but might be just a 2 position toggle.

Can you turn the power off to that circuit at the breaker box and remove the switchplate? Do you find a dimmer like device in there? or is it just switching between 2 other wires running up to the fan. If it's just a simple switch you can rule out any problems at that end (probably, switches do go bad, but if it's not heating and it continues to run the fan once the motor has warmed up a bit or gotten up to speed then it's not all that likely)

If thats the case then the problem is the motor. Either the bearings going or just needing some oil somewhere. I don't know any specifics about servicing those motors, if there is no manual attached to the thing and no info you can find here or elsewhere you should post some more questions about that and see what people can turn up.

[Wgoodrich]

One way to find out is by pass that switch and run the motor by the breaker in a test. If the motor runs correctly then that would eliminate the motor being a problem.

Just a thought

Wg