Furnace periodically won't start


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Old 02-12-07, 12:12 PM
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Furnace periodically won't start

My 6-year-old Lennox furnace won't always start up on its own when the thermostat calls for it to start. I would hear a relay click, but nothing else would happen and then it would provide a diagnostic code with LED 1 OFF and LED 2 a slow flash. I think I've traced the problem down to the combustion blower motor, which won't start its 15- second-pre-purge. If I just give the combustion blower motor a slight tape with a rubber mallet (typically I'll just turn the furnace off and back on to get the cycle to start over), it motor starts up and the furnace works fine until some later time when the motor decides not to start again and I repeat the process.

What kind of things break in a motor like this? Brushes, contacts, do the red/black/white wires come lose internally to cause an intermittent? Do I need to replace the motor or can I possibly repair it? It's a Fasco 7021-9884.
 
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Old 02-12-07, 04:24 PM
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You know if the fan has a hard time getting up to speed? or do you hear water splashing around inside?
 
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Old 02-12-07, 04:27 PM
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Do you have a supply house by you that will sell cash over the couinter? Some are kind of persnickety around here as to who they will sell to; i.e., licensed contractors, or people that have accounts set up for... like rentals or commercial businesses where the maintenance man can go there and get one on account.

These Fascos are sort of a disposable motor. But in many cases a supply house may say that you have to buy the entire ventor unit (motor/blower wheel/ housing assembly.)

If you are good at disassembling things, you might get the motor through a motor shop also.

A lot of the ventors I have worked on have the housing assembled in two halves where you pry off these metal clips that hold the halves together. Then, you have to remove the fanblade from the motor shaft so you can get the motor off. But getting the fanblade off the shaft without btreaking it can be tricky. The fanblade is most likely brittle plastic, held on by a metal clip that you must spread apart.
 
 

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