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Heath, HVAC Technician
Category: HVAC
Satisfied Customers: 1034
Experience:  11 yrs. comm.resid. service, Type III Cert.
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Why my furnace blower only works in ON position and not Auto?

Customer Question

My furnace fan/blower will not work when set to the auto position. However, the fan will work when the thermostat is set to the ON position. Also, the furnace is hot and the gas is burning. When I do turn the fan to the ON position, no hot air is blowing out of the vent. Just cool air blows. I replaced the thermostat and get the same results.
Submitted: 5 years ago.
Category: HVAC
Expert:  Heath replied 5 years ago.
Heath : Hello, the blower motor will need to be changed as the fan speed that is on the heat is burned out. The one for the ON position is a different speed. You could look in the furnace and locate the blower wire that is on the heat terminal of the board and then find one that is on park and switch the two and see if the blower runs. If it does, then the motor is bad. If not then the board is bad and not getting power to the heat winding of the blower.
The wires from the blower go to the circuit board in the furnace. Turn off the power before you switch the wires. There is one indoor blower that is what I am talking about and it is a 3 or 4 speed motor. If the speed that is on heat is burned out and the other speeds are okay you may be able to use another speed. That is what I am trying to get you to switch the wires for.
Customer : Ok. I'll try what you are suggesting. I'll let you know. Also, is it a big deal to change the motor if needed? I'll let you know in the AM.
Heath : No its not that big a deal to change the motor. The worst part is getting the squirrel cage off the motor shaft. But I can get you through it.
Customer: Hi, I found the red wire under an angle flange protector and switched with both the brown and yellow unused wires. Neither one would work, so I'm assuming the blower motor is shot. Although I think I can r/r the blower motor, I think I'll have a professional take care of that. Tell me what you think.
Heath : Yes the blower motor is shot. You will need to replace it. Its really not that hard to change. The worst part is getting the squirrel cage off the shaft of the motor.

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