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Could be a bad blower motor or start capacitor. Do you have power to the blower?
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.
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.
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.
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
No problem I will be here all day tomorrow and we can go from here
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.
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