Furnace's indoor blower's motor won't spin up without help

ArthurPeabody

My furnace (a Bryant 574D package unit) stopped working. I can hear the gas light and a motor hum. I hoped it was dirty, but it was clean. The LED is on, not flashing. The indoor blower, the fan that moves air in and out of the house, wasn't spinning. I spun it up by hand. It took a few seconds to get to a constant speed but makes no noise: no screeching, scraping, groaning, rumbling, or banging: it sounds as a motor should.

I let it spin down, but it wouldn't spin up on its own - so I left it on all the time. I think it moves air a little more slowly that it did before, that it takes longer to heat up my house. I turn the heat off at night, and it can get down to 50. If the heat stays on too long, as it may when warming up after a cold night, the gas'll go off and I'll get no heat. When that happened I gave it a rest for 10 minutes. Now I step up the morning temperature in smaller increments. It reaches a comfortable temperature eventually. I used to live in a cabin in the mountains, heated with wood, would wake up to everything frozen, so I don't really mind 50.

Is anything wrong other than the indoor blower's motor? Did windings short?

Mosherd1

Sounds like the capacitor has gone bad.

mattmia2

capacitor

probably isn't running at full speed with the bad cap so it shuts off the burner on high limit because it isn't moving enough air

EBEBRATT-Ed

I would remove the motor capacitor (it's mounted remotely from the motor usually) and usually has two wire going to it. usually oval but sometimes round. it helps the motor start. When you spin the motor your taking the place of the capacitor.

If you have a meter you can check the capacitance or just but a new one they are fairly cheap and the fact that the motor does run points to the cap as the most likely cause.

Derheatmeister

They also call them "Start Capacitor"
As EBEBRATT-Ed said when you spin the motor you are taking it's place..
It has nothing to do with a full speed not being reached,not reaching full speed is a indication that the Motor is going out!

Carefull that blower wheel can shred your fingers !

My experiance with this situation is that 8 out of 10 times you probably will need to replace both the Motor and of course when you change the motor you should repl.the Capacitor as well.

Sometimes ..IN EMERGENCY SITUATION ONLY We install a short lived "Hard start" capacitor as this one from Supco..






Again..In emergency situations and only just to get the heat going couple more times until proper repairs/replacements can be made.

HVACNUT

@Derheatmeister, you put boost caps on blower motors? 
And it's a run capacitor on most residential motors, not start caps.
In the odd event I don't have the correct capacitor, I stock a couple Turbo caps.

JUGHNE

Run caps as on the blower motor are always in the circuit passing current.
They help to start and then improve motor efficiency.

But a start cap is designed to be in the circuit for only 1 second or less.
If left in a circuit as if it was a run cap they can explode.
This memorable event occurred about a foot from my head, many years ago,
but was an immediate lesson in the function of start caps.
Always remembered.

ArthurPeabody

An oblong capacitor is mounted on top of the blower's enclosure. I shorted it out through my arm when I put my hand on the top of the fan - it was a pretty good spark.

If the blower only needed help spinning up I'd think it was just the capacitor, but the weakness of the flow (I tried with the filter off) and that the plenum got so hot the gas turned off before the thermostat reached temperature makes me suspect the motor.

The ducts are clean. The unit is 15 years old.

Thanks for all the help.

mattmia2

If it is a capacitor run motor it will not develop as much power with a bad capacitor and will run at a lower speed than with a good capacitor. If the capacitor is completely open or high resistance it is like running it with the 90 degree offset windings removed.

JUGHNE

Most likely if you install a capacitor it will fix things.
Look for a number of microfarads, might be something in the single digits.
This would be followed by 370 or 440 VAC or 370/440VAC.

Wire placement does not matter. There are only 2 terminals.
If 2 wires on one terminal do the same 2 wires on one terminal.

You must have the blower door on for the motor to get to full speed.

Let us know how this works out for you.

Recommended to get a new one not made in China. Mexico not bad.

JK_Brown

Since your description of shorting out the cap didn't include a description of the pain, that's a sign it's the capacitor. It still holds a charge, but not enough to bite. It would be charged at high voltage, so would make a good spark even if weak on charge.

The run cap on a PSC motor provides both the start offset and "tunes" the motor for most efficient running. The motor will run hot with a bad cap leading to motor failure.

Just get one of the same capacitance and the same or higher voltage rating. SupplyHouse.com is quick and easy.

mattmia2

I think they touched it while it was energized, probably while tiring to get the motor to start.

Get made in US of Mexico caps. I have had good luck with the titan HD caps. i have had some low quality caps fail in a couple years.

tim smith

Capacitor most likely. If you have a meter with uf or mfd for selector switch disconnect wires and test across terminals. Should be close rating on cap. 5, 7.5 or 10 most likely.

ArthurPeabody

A new capacitor did the trick. The old one is bulging. Unfortunately, because it was hard to get to, I accepted the book value for the cap, 5 μf. It turned out to be 15 - but it works well, not just starts up but blows as well as it used to. I'll get a 15. Thanks for all your help. It is a run cap, not just for start.

mattmia2

It will probably be ok on low speed for heat. on high speed for ac and sometimes for fan the motor might overheat with the smaller cap.

mattfolse

I have a similar problem if someone would care to offer some help….I know very little about electrical stuff. 

I have an RV with two roof mounted Coleman AC units. One works off of a thermostat for the entire unit and the other cools only the bedroom and is operated by a rotating switch. I turned on the unit with the rotating switch and the fan did not come on but I could hear it trying to start. I removed the filter cover and gave it a spin and it worked. 

Knowing a little about the function of a start capacitor my first thought was bad capacitor. In order to confirm this I swapped it out with the one from the unit that runs with an identical capacitor. 

It still does not start up without help but runs fine with a little spin. The motor runs quietly and spins freely. 

Any help would be greatly appreciated. 

HVACNUT

Without knowing the actual micro farad readings of the caps, it's hard to definitively rule it out, but it seems like a bad motor. Can you check amps while trying to start? Can you check resistance of the motor windings.