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dna48

Lennox G16 furnace: blower motor failure?

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dna48

We have a faithful old Lennox HVAC system, and yesterday our blower motor apparently failed.

The compressor on the roof (also Lennox, seemingly wired in correctly) will run as expected, and proceed to ice up the lines, and the indoor blower relay will make a nice click, but the motor will not start. it does not get hot, and it does not hum, and the squirrrel cage turns freely.

Investigating with my VO meter finds that the motor is getting voltage. It seemed at first that it was getting voltage on two different speed wires at the same time, but in fact it is only getting it on the black wire. Apparently, the black and red wires are shorted together inside the motor

that is, when I insert the Common probe into the wirenut for the Common that goes back into the wall, and touch the hot probe to the relay terminal that's supposed to energize the blower when cooling, i read ~110 volts

and when i touch it to the terminal that's supposed to be energized when heating, it also reads ~110 volts. But the terminal isn't actually energized (as I verified by disconnecting the blower from it) Nor is the wire from the fan control box that keeps it running until the heat exchanger cools. no, just the wire that supposedly feeds voltage into the blower motor

the only manual i've found for it is this one:

http://www.cozyparts..._03-01-1984.pdf

I'm hoping someone can tell me whether this means the motor has failed, or if maybe it's just one of the speed wires?

Oh, I forgot to mention. The fan doesn't turn on when in heat mode either. though this might not mean anything, since that's the wire that had voltage when i thought it shouldn't

Edited by dna48

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jumptrout

Your capacitor may have failed.

If you have a capacitor reader check it.

If not replace it.

If the fan motor has to be replaced the new capacitor could be used on it.

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dna48

Well, i checked the capacitor, and it was fine.

One thing I noticed but forgot to mention was that there was no continuity through the motor. Infinite resistance.

It occured to me that the thermal switch inside might have failed, so I opened the casing, and after cleaning out a bunch of dust and gunk, i saw a scorch mark on the thermal switch.

Apparently, one of the wires connecting to the switch had corroded, and broken, arcing into the switch, and burning a hole in the plastic sleeve it was wrapped in. Testing the rest of the motor, it seems that there is nothing else wrong with it. Now i've just gotta source a thermal switch.

It's a Klixon switch. Here's some pictures

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RegUS_PatOff

7AM (style)

033 (130C)

A (terminals on the same end)

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dna48

7AM (style)

033 (130C)

A (terminals on the same end)

Yeah, that's what I got, looking here. Thanks though!

apparently the 8 means that it has a tolerance of plus or minus 8°?

all the ones i've seen online have a 5 there (except this one, which is available in a 7 as well)

Any idea where I should go to get one? i was hoping there'd be a brick and mortar store in my area. Not sure what I should do to install it though. Maybe it's availlable with crimp on connectors?

Edited by dna48

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RegUS_PatOff

... apparently the 8 means that it has a tolerance of plus or minus 8°?

maybe, but I don't think it would matter, much.

Maybe try some local Motor re-building shop.

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