Burner but no fan
#1
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Burner but no fan
I have a carrier model 48SD and when I turn it on the burner starts fine but then the fan does not start. I have waited several minutes and it still does not run. If I turn it off and start all over again it will run just fine. It also will work fine for a long time and then for no reason it will call for heat and the fan will not start again. I am not sure what is wrong and hope someone can tell me what to repair, thanks.
#2
You'll need to determine if it's a control board problem or a blower motor problem.
When the fan does not start......try putting the AUTO/FAN ON switch in FAN ON mode and see if fan works then. If it doesn't come on then you have a blower motor issue......possibly a defective starting capacitor.
When the fan does not start......try putting the AUTO/FAN ON switch in FAN ON mode and see if fan works then. If it doesn't come on then you have a blower motor issue......possibly a defective starting capacitor.
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I waited till the problem happened again the fan was not working so I turned the fan on and it started so I guess it is not the fan. Any other thoughts before I get a new board.
#4
Most furnaces use a heat thermostat to turn the blower on. Yours does not. It's a timed function controlled by the control board. Based on the service schematic I would say it's a defective control board.
The board.....part # 325878-751 is pretty pricey.
I would wait for a confirmation from one of the HVAC guys.
The board.....part # 325878-751 is pretty pricey.
I would wait for a confirmation from one of the HVAC guys.
#7
Thanks.
I'm surprised to see a direct drive multispeed motor in a Carrier gas unit use the same speed for heating and cooling.
I looked up the 48GS that this unit resembles and it is the same.
I'm surprised to see a direct drive multispeed motor in a Carrier gas unit use the same speed for heating and cooling.
I looked up the 48GS that this unit resembles and it is the same.