Furnace Blower Motor question

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Russ H

Russ H

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HI All,

I hope this is the right place to post this question. I am noticing the blower motor on my forced air furnace seems to be struggling to start. It always does start but for the initial few seconds it sounds like it is straining. Any ideas what could cause this? I'm thinking maybe a weak capacitor. Any ideas, please respond

Thank you,

Russ
 
May not be your problem but over time the fins and every part of these get packed full of dirt. I pulled and cleaned mine after we got the house and by the look of it, it had never been cleaned before.

After a good cleaning it was smooth, quiet and got right up to speed when it turned on.

The difference was huge.
 
Replacing the cap might help but it's likely the windings on the motor.
How old is the motor?
What I like to do is switch the speed from low to medium by changing the wires on the circuit board.

By doing this sometimes you can determine if it's the windings.

Start the motor after you change speed and listen to see if the sound changes.

In my experience a blower that has dirt build up in its vanes has less resistance on it and a lower work load.
 
AlV said:
Replacing the cap might help but it's likely the windings on the motor.
How old is the motor?
What I like to do is switch the speed from low to medium by changing the wires on the circuit board.

By doing this sometimes you can determine if it's the windings.

Start the motor after you change speed and listen to see if the sound changes.

In my experience a blower that has dirt build up in its vanes has less resistance on it and a lower work load.
Click to expand...

That motor is about 12 or 15 years old. The vanes appear to be clean so I'll try changing the speed and see what happens.

Thank you,

Russ
 
If it happens to be a motor that can be oiled than that would help too. The plus might be hidden under some dirt if it has any. On mine the plugs are yellow.
 
Oklacarcollecto said:
If it happens to be a motor that can be oiled than that would help too. The plus might be hidden under some dirt if it has any. On mine the plugs are yellow.
Click to expand...
Good point.

I'd definitely look to oil the motor if it has ports.
 
Pull the motor / blower apart and simply spin it with your fingers. feel how "free" the shaft is. These are generally bushed, and not ball bearings. Note now it was mounted, IE vertical orientation. Punch small holes in the end caps "up" and use a "zoom" oiler or other device to inject 20WT or similar oil into the bushings. If they seem "free" that part is OK. Blow any dist / lint out of it if necessary pull the motor apart to inspect internally.

Don't be afraid to wash out the blower and housing. Use a hose, detergent. That is what your dirty jeans are for

If the motor does turn free, there's only two things left............voltage, that is, the switch / relay contacts, and the cap

You can easily check the switch contacts. Be careful, as these are usually multi speed with only two hooked up. That is, example, the "red" hooked up for low speed on heating, and the "black" hooked up for high speed on high speed on A/C or "summer" fan There may be a couple of "in between" speeds, yellow, blue, unhooked, taped off

So get the thing in a position where you can run the blower. You MUST run the blower with the compartment CLOSED OFF. The blower draws too much current with the blower compartment OPEN. You must run it in a "normal" configuration. So look beforehand and "rig" a meter in such a way that you can measure voltage to the blower terminals to determine if the switch is delivering full voltage. Additionally if you have a clamp on ammeter, you can check load current

If the thing is getting full line voltage and won't start correctly, I'd try a new cap.

As you guys know, I'm NOT a guy who advocates "throwing" parts at a problem, but if you really suspect this, and the bearings are free, this would be one of those times. Caps are cheap. Make certain you get one the correct rating. You want the correct "microfarad" and AT LEAST the same or more AC voltage. It can be for more voltage but not less.

You do NOT want very much deviation, either more or less, on the microfarad rating

Don't however, expect these motors to rip up to speed. These are a low torque device, especially on the "low" heating speed, and normally take several seconds to do so. Stop and think if it's 'acting normally' or if things have changed. Have you noticed any smell, IE is the motor running hot?

ALL of this used to be part of my normal service routine. Some of my customers were amazed. "None of these other guys ever............." I guess they must 'ove just stood there and LOOKED at it then LOL
 
AlV said:
Replacing the cap might help but it's likely the windings on the motor.
How old is the motor?
What I like to do is switch the speed from low to medium by changing the wires on the circuit board.

By doing this sometimes you can determine if it's the windings.

Start the motor after you change speed and listen to see if the sound changes.

In my experience a blower that has dirt build up in its vanes has less resistance on it and a lower work load.
Click to expand...

That motor is about 12 or 15 years old. The vanes appear to be clean so I'll try changing the speed and see what happens.

Thank you,

Russ
 
67Dart273 said:
Pull the motor / blower apart and simply spin it with your fingers. feel how "free" the shaft is. These are generally bushed, and not ball bearings. Note now it was mounted, IE vertical orientation. Punch small holes in the end caps "up" and use a "zoom" oiler or other device to inject 20WT or similar oil into the bushings. If they seem "free" that part is OK. Blow any dist / lint out of it if necessary pull the motor apart to inspect internally.

Don't be afraid to wash out the blower and housing. Use a hose, detergent. That is what your dirty jeans are for

If the motor does turn free, there's only two things left............voltage, that is, the switch / relay contacts, and the cap

You can easily check the switch contacts. Be careful, as these are usually multi speed with only two hooked up. That is, example, the "red" hooked up for low speed on heating, and the "black" hooked up for high speed on high speed on A/C or "summer" fan There may be a couple of "in between" speeds, yellow, blue, unhooked, taped off

So get the thing in a position where you can run the blower. You MUST run the blower with the compartment CLOSED OFF. The blower draws too much current with the blower compartment OPEN. You must run it in a "normal" configuration. So look beforehand and "rig" a meter in such a way that you can measure voltage to the blower terminals to determine if the switch is delivering full voltage. Additionally if you have a clamp on ammeter, you can check load current

If the thing is getting full line voltage and won't start correctly, I'd try a new cap.

As you guys know, I'm NOT a guy who advocates "throwing" parts at a problem, but if you really suspect this, and the bearings are free, this would be one of those times. Caps are cheap. Make certain you get one the correct rating. You want the correct "microfarad" and AT LEAST the same or more AC voltage. It can be for more voltage but not less.

You do NOT want very much deviation, either more or less, on the microfarad rating

Don't however, expect these motors to rip up to speed. These are a low torque device, especially on the "low" heating speed, and normally take several seconds to do so. Stop and think if it's 'acting normally' or if things have changed. Have you noticed any smell, IE is the motor running hot?

ALL of this used to be part of my normal service routine. Some of my customers were amazed. "None of these other guys ever............." I guess they must 'ove just stood there and LOOKED at it then LOL
Click to expand...

Very good information, I'll try all you said..........

Thank you very very much..............
 
AlV said:
Replacing the cap might help but it's likely the windings on the motor.
How old is the motor?
What I like to do is switch the speed from low to medium by changing the wires on the circuit board.

By doing this sometimes you can determine if it's the windings.

Start the motor after you change speed and listen to see if the sound changes.

In my experience a blower that has dirt build up in its vanes has less resistance on it and a lower work load.
Click to expand...

Russ H said:
That motor is about 12 or 15 years old. The vanes appear to be clean so I'll try changing the speed and see what happens.

Thank you,

Russ
Click to expand...

Sorry I completely disagree with this assessment

If it's a winding problem, it would likely be smelly. "Changing windings" would not fix it, as "speed" is not independent but rather inter-linked taps of part of the same winding. Windings generally don't go bad unless they have been overheated for some reason, and usually that reason is some external cause such as bad bearings or a bad cap, bad starter ( in the case of a centrifugal start switch, etc) I've got a lathe motor that must be 60 years old.
 
marksmopar1 said:
For the $80-$120 if that cost of a new motor,,,,,why mess around, replace it..done :)
Click to expand...

Some of us like our money. Last furnace issue I had (over 2 years ago) was the failure of a $157 part. More specifically, one small part of that $157 part was not soldered very well from the factory.

Instead of spending $157, I fixed it in about 4 minutes for nothing.

Doing stuff like this is one reason I was debt free including the house at 42 years old.
 
67Dart273 said:
Sorry I completely disagree with this assessment

If it's a winding problem, it would likely be smelly. "Changing windings" would not fix it, as "speed" is not independent but rather inter-linked taps of part of the same winding. Windings generally don't go bad unless they have been overheated for some reason, and usually that reason is some external cause such as bad bearings or a bad cap, bad starter ( in the case of a centrifugal start switch, etc) I've got a lathe motor that must be 60 years old.
Click to expand...

Its okay if you disagree and normally I would leave it at that. :)

In this case I feel obligated to elaborate further to provide clarity and mitigate confusion.

My methodology has served me well for many years as I am sure yours has served you (it is one way to skin a cat). These are not digital answers but rather analog and because of the analog nature of these electric motors there is a bit of an art to the science.

Keep in mind the duty cycle of your lathe isn't the same as a household furnace, and not all motors are created equal. As you state, external variables can have a negative impact on a healthy motor and over the course of time (in this case 15 yrs) cause it to get tired.

Line speed taps on the motor winding are precisely the reason I suggested a quick diagnostic technique.

The thinking: If the low speed tap uses most of the winding because it its the first tap in the line.. it's possible that the winding section closest to the tap has been stressed and fatigued. By switching to a different speed tap you can possibly move up the line passed the fatigue section. (of cours this presumes proper voltage is supplied to the motor).

I suppose i could have just asked if Russ (the OP) had the same experience starting the motor when he turned the fan switch on at the thermostat (Effectively placing it into the high setting)

In any case if it were me I would, switch speed and check start the motor running a normal heat cycle. (note: I would use an amp clamp if I had one but if I didn't I would still perform these steps.)

If the issue persisted I would replace the cap and try again.

If the issue went away I would change back to low and cycle it again.

If it came back after switching to the low tap, I would not use low speed and switch to the medium tap then buy a motor.

If it doesn't return after replacing the cap and switching back to the low tap I would leave it knowing that a motor purchase is in my future.

That's just one approach.

-AlV
 
Yet another opinion. Owning a Heat and air shop for the last 10 years has given Me a bit of experience. Usually I would 1)check voltage at the motor leads first, 2) meter the capacitor(mf, uf, or farads setting on meter if equipped, most blowers have a 12.5, 15, or 20 mf cap. Unplug leads and discharge by grounding, look on the cap for value). 3) Check amp draw on blower motor. If a meter is not available, and the motor turns freely and keeps spinning when given a push, swap the capacitor ($10-$20) If the motor does need to be replaced, make sure the amp rating matches or exceeds the original, and install a correct new capacitor.
 
replace the capacitor (starter) I had same problem
 
Well.....I say get a new motor...of course after checking the usual's out. I am Foreman of an HVAC shop, as well as Industrial Mechanic, Power Engineer, Gas licence ..done many of these :)

Some things are just not worth the time....But always worth checking out, after all it does come down to trouble shooting -do that first it's free. Never toss parts at it.. I like my $$$$$ as well, LOL
 
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