Fan not starting in ON position, but working in heat or ac mode


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Old 05-18-13, 10:18 AM
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Fan not starting in ON position, but working in heat or ac mode

I have a curious problem. My blower fan does not come on in the ON position. When on AUTO it turns on when the heat kicks in or when in cooling mode. So - fan is not broken, but not controllable through thermostat. I have jumpered the R and G wires inside the furnace to eliminate problems with the thermostat or the cables to the furnace - fan does not come on. Unit is a LENNOX unit. Circuit board was replaced last year. Circuit board gone again?!? Wiring to the fan motor bad?

How can I test the signals from the circuit board to the fan? There are 4-5 cables going to the fan from the circuit board.

Thanks!
 
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Old 05-18-13, 11:16 AM
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Welcome to the forums.

If the AC activates the fan properly that would mean the connection (green wire) between the thermostat and the air handler is ok. It would suggest that there is a problem with the thermostat not applying power to the G terminal when in FAN ON mode.
 
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Old 05-18-13, 11:18 AM
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Some lennox control boards have a separate terminal for continuous fan. Does your board have this terminal? Is a wire plugged into it?
 
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Old 05-18-13, 07:26 PM
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Simple answer once you got it: I have a 4 speed fan and the two cables for heat and ac were connected, the other two were hooked up to the PARK connectors. Once I moved one of them to FAN the fan worked. Must have been connected wrong when the circuit board was switched out a year ago. I must have never noticed...
 
 

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