troubleshooting furnace fan (only runs if I give blades a spin.)

[pjstock]

this might be electrical but I thought I would start off in HVAC. We have recently installed a wood burning fireplace in a country home. The house has duct work running throughout (to distribute heat and cool from the original thermostat controlled gas fireplace and A/C system.) The gas FP has been removed and we never use the A/C so all we really want to do now is have a simple On/Off switch for the fan in the duct work to blow the wood stove heat around. No thermostat is required. During some renovations this spring we removed the thermostat and the original on off switch for the blower fan. Now, with winter approaching we woudl like to get the blower blowing again. WIth everything reconnect the way I think it was originally (I am something of an electric moron.) all I hear is a hum from the blower unit. When I connect the blower fan directly to power (bypassing a capacitor on the side of the blower unit and the circuit board that I believe controled the thermostat), the fan runs fine. As long, that is, as it has some motion already. So, if I give the fan blades a bit of a spin and then flip the Power switch, it takes off and blows. However, if the fan is stationary/still and I flip the power switch, all I hear is that same hum. It doesn't start. Is there something in a blower fan system that gives it a kick start that I am replicating with my hand start? any clues? Thanks Peter

[HayZee518]

blower motor

check on top of the motor for a start or run capacitor. sounds like the start capacitor is shot. maybe just the wires come loose. the brown or brown/white and white neutral connects to the capacitor. if you need a new capacitor the voltage can be higher NOT lower than the original. the microfarad rating needs to be equal or slightly larger but not by a whole scale.

[pjstock]

what does a capacitor do?

please excuse my ignorance, but what does the Capacitor do in this setup?

[HayZee518]

blower motor

your motor is called a split phase induction motor. the rotor is made up of iron laminations called "punchings" stacked one on top of the other and shorted out on both ends with aluminum castings. the field is copper windings wired in series aiding. the capacitor upsets one phase of the winding and causes the rotor to spin in one direction. the way a motor operates is it is always trying to catch up to a rotating field in the windings and so imparts a rotation on the rotor.

[HayZee518]

blower motor

your motor is called a split phase induction motor. the rotor is made up of iron laminations called "punchings" stacked one on top of the other and shorted out on both ends with aluminum castings. the field is copper windings wired in series aiding. the capacitor upsets one phase of the winding and causes the rotor to spin in one direction. the way a motor operates is it is always trying to catch up to a rotating field in the windings and so imparts a rotation on the rotor.
the field imparts a magnetic field in the rotor which is opposite to the field winding itself.

[pjstock]

thank you. that's so clear. I did bypass the capacitor when I direct wired the fan motor. I might redo the test including the capacitor (and bypassing only the circuit board) to see if the capacitor is good or not. But thanks. What a resource!

[pjstock]

photos and drawing

Went back down to look at things and decided that I had better not tinker more with something I so poorly understand (Capacitors etc.) (Curiosity + ignorance usually = trouble ) So, here are some photos that might shed some light for someone actually knowledgeable. I'll now read up on Capacitors but, if you look at the wiring "picture" (I wouldn't grace it with the label "diagram") I am wondering why there is only one input (Purple to A) to the capacitor but apparently two outs (Purple from B and Brown from D.) when I hardwired my electric leads (X,Y) yesterday, I (maybe foolishly) wired them to B and D. and that resulted in the fan running when I spun it. can you figure out anything from these photos and sketch.? Can anyone tell me how I can test that Capacitor? Or how I would wire it up to the live power to test the system with the capacitor IN but the circuit board Out.? Though on the other hand, I don’t want to do something boneheaded that might cost me a $300 fan. Peter Toronto, Canada

[HayZee518]

motor

ok, looking at your photos, the brown goes into the motor, the larger purple goes into the motor, the small bright blue is 120 volt motor speed to the hi-lo-med connector block. the small bright purple looks to be the neutral. the two designations you give F & G are on the motor board. I'm gonna try to find this motor from what I see. the numbers I see are XSS 31 WMV - I'll check out grainger replacement motors first then go to my HVAC blower motors. thermostat connections are usually marked TH-TH on a control board. Motors have T1 & T2 for connections. Line input are L1 & L2.

[HayZee518]

blower

what make is the furnace? this will narrow it down somewhat. my sources page lists 108 pages of 15 motors per page. I went through 22 pages looking for a motor with a speed block on it. the numbers xss 31 wmv doesn't jive with what's listed.