Blower motor intermitantly fails to spin


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Old 02-17-08, 02:03 PM
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Blower motor intermitantly fails to spin

Hi!

Just an average homeowner here...

Beginning about a month ago, the blower motor in my 20 year-old gas furnace (Carrier model #394J060095) began having trouble turning. A minute or so after the burners fire-up, the motor normally starts to turn the blower. Lately, I'll hear the motor hum, but it won't turn the blower. I can jump start it by removing the front cover and manually giving the blower a spin and replace the cover. We don't run it unless I am around to do this if needed (we live in Southern California).

Yesterday I removed the blower/motor unit and lubricated both motor ports (I did this in the middle of a very cold night last year also after the first incident, but used 20W motor oil I had on-hand). The front port had plenty of oil in it, but the back did not.

Last night, it worked fine 3-4 times throughout the evening, then failed on the last attempt before we shut the furnace off for the night. I'm afraid I only added 2 drops of newly purchased all-purpose turbine oil, thinking I had read that somewhere. Today I dug up my old maintenance instructions and read that it will hold 16-25 drops.

My question is, do I need to pull it out again and add more oil, or is there some other cause for this failure, like the capacitor? If so, how would I test that?

Thank you very much!

Todd
 
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Old 02-18-08, 04:36 PM
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First report back to us your finding that if [make sure furnace switch is turned off!] you give the squirrel cage a twirl, that it can keep spinning for at LEAST 10 seconds without coming to a stop.
 
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Old 02-19-08, 02:24 AM
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Lube as your manual recommends and also throroughly clean-up the fan wheel.

And as Ecman says, proceed then to check and see if the fan wheel spins nicely...else...the bearings may be on their way out.
 
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Old 02-20-08, 01:46 PM
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I would definitely try putting in a new capacitor. That's typical for capacitor failure (will run if started by hand).

Caution!! The old capacitor may still have a charge even after power is disconnected!
 
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Old 02-22-08, 04:56 PM
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Thank you all!

Yes, the squirrel cage spins freely for about a minute. So it sounds like the capacitor then? Is there a way to test that?
 
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Old 02-22-08, 07:13 PM
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There are half-arse ways to sort of guess, like by putting voltmeter test leads on the terminals of the capacitor and seeing if the reading goes up, then slowly lowers (probably is good then, but I guess not a certainty). And seeing if the capacitor is bulged out, or any other physical characteristics. [Be careful handling a capacitor as they retain a high electric current when good.]

You can find writings and drawings on testing capacitors on the web, where you hook up a 100 watt light bulb in series and other stuff.

If no other better answers than mine here, you can ask some guy at a motor shop, if you don't care to check out what's on the web. I have actually looked this information up already in the past but cannot remember precisely how the test is carried out. My problem is I know a motor shop owner to well and it's too easy for me to take stuff to him.

You could also have something wrong/shorted going on in the motor itself. A quick check would be to disconnect the motor wires, then hold voltmeter at ohms setting with test leads going between hot and neutral (white motor wire) of motor wires. Try all the colored wires by testing one at a time with your voltmeter set to ohms and put one test lead on one of the colored wires and the other onto the white (neutral) wire of the motor. Then, do basically the same type of test except instead of putting the other test lead to the neutral, put the test lead onto the motor housing to see if motor current is going directly to ground. If you get a reading on ANY of the tests I mentioned, the motor is shot.
But this test only works if the motor wires are disconnected.

.............

You could always go to the a/c-d/c electrical forum here and ask the electricians about the capacitor, also.
 
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Old 02-22-08, 08:47 PM
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Very helpful and informative ecman51 - thank you very much, I appreciate you for taking the time to answer my question so thoroughly.
 
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Old 02-23-08, 03:54 PM
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Originally Posted by ecman51` View Post
A quick check would be to disconnect the motor wires, then hold voltmeter at ohms setting with test leads going between hot and neutral (white motor wire) of motor wires. Try all the colored wires by testing one at a time with your voltmeter set to ohms and put one test lead on one of the colored wires and the other onto the white (neutral) wire of the motor.

..... If you get a reading on ANY of the tests I mentioned, the motor is shot.
Sorry. I just caught this. I made a mistake here. You SHOULD get a reading, with only slight resistance, for this test! Sorry. If you got no reading, THEN the motor would be dead, as that would indicate a hot winding to neutral was burned up.

But on the other test from the colored run- wires to the metal casing of the motor -THAT should have no reading, as mentioned.
 
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Old 02-23-08, 06:24 PM
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I appreciate that - thank you for your correction. I thought that's what you meant, but wasn't sure. :-)
 
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Old 02-23-08, 06:47 PM
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Capacitor

For the price of a capacitor, just replace it. Any electric motor shop can test it & that's generally a good place to find almost any cap you need. Simply match the f (or mf) rating & the voltage. Note: Voltage can be higher but not lower (you can use a 440 in place of a 370 but not the other way around). Capacitance (f or mf) must be within 10% of the rating.
 
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Old 02-24-08, 06:07 AM
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mitchellbd

you can try a new capacitor but i feel that what is going on is the start of the motor bearing going bad.
the motor has a sleeve bearing thus the need for lubrication.
The sleeve bearing weares a little egg shaped after years with no oil. After it weares oil won't help. Allthough the blower spins free without power after a short period of time running the bearing gets hot and expands a bit allowing the motor rotor to get to close to the motor stator (windings)
and the magnetic field will pull the rotor too close to one side and stop. Let the bearing cool and it will run again untill it heats up again.
The trick is to put oil in the motor about every year before it fails.
You will need to replace it.
Most blower motors are offered in both sleeve or ball bearing.
Go with the ball bearing. You never need to oil it.
 
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Old 02-24-08, 01:33 PM
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Originally Posted by mitchellbd View Post
The sleeve bearing weares a little egg shaped after years with no oil. After it weares oil won't help. Allthough the blower spins free without power after a short period of time running the bearing gets hot and expands a bit allowing the motor rotor to get to close to the motor stator (windings)
and the magnetic field will pull the rotor too close to one side and stop. Let the bearing cool and it will run again untill it heats up again.
Yes. Very good advice.

But then he should be able to grab the blower wheel cold, and then maybe hot also, and try to wiggle it up and down, and to not be decieved by feeling a clunk in the end-play. It is imperative that when trying to wiggle the shaft that one tries to wiggle when first pulling out on the shaft and keeping it there, and perhaps also pushing it in and keeping it there, while trying to wiggle the shaft. If a person feels any of that clunking feeling, time for new motor for reasons poster said.
 
 

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