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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8172
Experience:  Furnace, A/C and heat pump specialist.
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My lennox gas furnace ignites but the blower does not come

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Hi, my lennox gas furnace ignites but the blower does not come on. I can spin the blower by hand but it does not turn on when I flip the thermostat fan switch to on.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

Could be a bad blower motor or start capacitor. Do you have power to the blower?

Customer: replied 6 months ago.
The power to the furnace is on. I can see LED lit up on one of the boards. It seems that the blower comes on intermittently when I flip the switch to on on the thermostat.

You need to test the power to the blower motor when it should be running. That's the only way to be sure of the culprit.

Customer: replied 6 months ago.
OK so how do I do that

You need a voltmeter to probe the leads to the blower when it should be running. The easiest way to do this is to put the thermostat fan switch to ON. Be sure you hold the blower door/panel switch in while you do or there will be no power to the unit.

Customer: replied 6 months ago.
I switch the thermostat fan two on after 30 seconds or a minute or so the blower kicked on so it must have power to it

I'm going to open this up to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

If blower came on that tells us motor is good. Give me the model on furnace so I can see if motor is controlled by a relay ot a control board.If a control board the board is failing and needs to be replaced as the built in relay is sometimes not closing when it should.

Customer: replied 6 months ago.

Let me gab a manual

Thanks for your patience.Your fan relays are built onto a little circuit board. These little black boxes on the board are the relays. They can not be replaced individually but will probably need to replace the BCC board.

To verify board is the problem, When fan should be on and will not come on, check between Neutral and A in fan mode or Neutral and H in heat mode to see if board is sending 120v to motor

These are the relays that tell fan to come on.They can stick closed and cause fan to run nonstop or stick open no sending signal to fan

Customer: replied 6 months ago.
Ok I will check for voltage. Not home at the moment. Will check late tonight.

No problem I will be here all day tomorrow and we can go from here

Customer: replied 6 months ago.
No power at H

OK the BCC (Blower control board) is going to be the problem.

You will need to replace that little board

You might Google part number 48K98 and find a better price

If you have further questions, please let me know.

Thanks for letting me work with you.If my answer has been polite, professional,and thorough, please click one of the ratings before you go. If you still need help let me know!.Expert is not paid for assisting you until you rate answer.Feel free to follow up for 30 days at no additional cost. Bonus always appreciated if you feel justified.

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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8172
Experience: Furnace, A/C and heat pump specialist.
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