Squirrel cage furnace motor - Electrician Talk - Professional Electrical Contractors Forum

splinetto · 07-20-2009, 06:03 PM

Im not up on motor troubleshooting....Hence the question...What would cause the blower to cut out in the middle of a cycle....Bad capaitor?....

MDShunk · 07-20-2009, 06:06 PM

More often than not, bad fan center relay or bad control device (thermostat).

If it's one of the newer GE ECM motors, there's a hundred more things it could be.

drsparky · 07-20-2009, 06:08 PM

The capacitor is for starting only.

splinetto · 07-20-2009, 06:18 PM

Quote:

Originally Posted by MDShunk

More often than not, bad fan center relay or bad control device (thermostat).

If it's one of the newer GE ECM motors, there's a hundred more things it could be.

Not new at all.....However I did install a new T stat a year ago....The problem is it runs ok for a day or two and then itll shut down..........So if I install a new or jumper the t stat I wont know if it fixed it .........I did notice the fan itself was hard to spin when it shuts down.....Would that point to the bearings......I really need to take a class...

MDShunk · 07-20-2009, 06:20 PM

Quote:

Originally Posted by splinetto

Not new at all.....However I did install a new T stat a year ago....The problem is it runs ok for a day or two and then itll shut down..........So if I install a new or jumper the t stat I wont know if it fixed it .........I did notice the fan itself was hard to spin when it shuts down.....Would that point to the bearings......I really need to take a class...

Hey man, these furnace blower motors are about 30 bucks at the supply house. If it's got tight spots, replace it on spec. Tight spots is a good enough reason to replace a motor, even if it's not a motor problem causing the shutdown. You really need to be there to see if there's power on "G" and if the motor is getting power when it's not running (and it should be). Without being there, replacing an otherwise cheap motor that presently has tight spots is a perfectly reasonable thing to do. Always, always, always replace the cap when you're replacing any cap start motor.

splinetto · 07-20-2009, 06:30 PM

Thanks Marc

Peter D · 07-20-2009, 07:23 PM

I wanna be like Marc when I grow up.

lectricboy · 07-22-2009, 11:29 AM

Quote:

Originally Posted by drsparky

The capacitor is for starting only.

Some single phase motors have a start capacitor and a run capacitor.

MechanicalDVR · 07-22-2009, 11:54 AM

Check the amp dram on the motor with the fan compartment closed. See if the airfilter is clean if that the motor isn't getting enough air over the windings to cool it.
You coulod check the amp draw on the fan center relay but that isn't the place I would start here.

MechanicalDVR · 07-22-2009, 11:56 AM

Quote:

Originally Posted by MDShunk

Hey man, these furnace blower motors are about 30 bucks at the supply house. If it's got tight spots, replace it on spec. Tight spots is a good enough reason to replace a motor, even if it's not a motor problem causing the shutdown. You really need to be there to see if there's power on "G" and if the motor is getting power when it's not running (and it should be). Without being there, replacing an otherwise cheap motor that presently has tight spots is a perfectly reasonable thing to do. Always, always, always replace the cap when you're replacing any cap start motor.

True some of the basic motors are only @$30 there are some that maybe closer to $200, it depends on a few factors, I'd hate to be wrong on the higher end ones. Call backs can ruin a great rep in no time flat.

KayJay · 07-22-2009, 05:47 PM

Damn… I’d like to know where your getting two-speed NEMA 42Y & 48Y blower motors for $30.00, because I want to start shopping there!

Even the MasterFit ones start at around $80.00 here, and that doesn’t even include the mounting ring or cap.

MDShunk · 07-22-2009, 05:59 PM

Quote:

Originally Posted by KayJay

Damn… I’d like to know where your getting two-speed NEMA 42Y & 48Y blower motors for $30.00, because I want to start shopping there!

Even the MasterFit ones start at around $80.00 here, and that doesn’t even include the mounting ring or cap.

APR Supply. Don't know if you have them in your area or not, but they are a chain.

cmec · 07-22-2009, 08:30 PM

LOOK at the fan and limit controll, especally if it has push in connections pull and push on them and look for discoloration.

KayJay · 07-23-2009, 05:32 PM

Quote:

Originally Posted by MDShunk

APR Supply. Don't know if you have them in your area or not, but they are a chain.

Thanks for the link. Seems they have 22 branches, which is substantial, but all in the PA area. Looks like they do offer online ordering though, so even with freight, they may still be cheaper than suppliers in this area.

jwiehagen76 · 07-24-2009, 10:40 PM

Most residential furnaces utilize a psc motor or permanent split capacitor. The capacitor stays in the circuit. the cap is in series with the start winding. you may have a bad cap or a bearing the heats up and mtr drops out on internal ol

Toronto Sparky · 07-25-2009, 01:18 PM

Thermally protected motors have a thermal cutout switch inside that kills the power on overheat , once it cools it restarts.

MDShunk · 07-25-2009, 01:19 PM

Quote:

Originally Posted by Toronto Sparky

Thermally protected motors have a thermal cutout switch inside that kills the power on overheat , once it cools it restarts.

That's what makes me feel pretty good about replacing the motor as the fix, since he says it has tight spots when you spin it by hand.

iamatt · 08-21-2009, 07:55 AM

Quote:

Originally Posted by splinetto

Im not up on motor troubleshooting....Hence the question...What would cause the blower to cut out in the middle of a cycle....Bad capaitor?....

Before I get blown out of the water. I did not see the other posts...
Good advise guys.

Thermostat is not usually the answer.
When you are there at the furnace check your voltage in and out from the circuit board.
If this unit is failing all the time you should be able to see voltage drop from the board to the motor.
If that is the case you know what is wrong.
Cap tester will tell you if that needs replaced.
Baring that check the amperage from the blower motor. See if it is over drawing.
The motor could be going off on thermal protection.

Richard Rowe · 08-21-2009, 09:36 AM

I would run the blower motor for 30 min then check the bearings to see if they are hot and while your doing that have a meter checking the amps. If the bearings are bad then you should be able to tell after 30 min. Just be sure it is like normal operation, all panels on no extra ventalation. If it quits you will be able to find it.