erratic behavior of blower fan

Old 10-06-11, 11:45 AM
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erratic behavior of blower fan

Hi folks:

I have a Dayton forced air furnace, approximately 7 years old. The issue I've been having is that the fan runs for an extended period of time after the burner shuts off. There are times when it shuts off within a reasonable amount of time, and other times where it seems to run for hours, essentially blowing cold air. The fan also comes on too early. Clearly a temp related issue. I'm thinking limit switch.

Unlike my other furnace in the house, this one does not seem to have a control box with the manual on/auto button. The only thing I see related to the fan is a small timer, adjustable from 60 to 200 seconds on the fan motor housing. This was adjusted from near maximum to the halfway point, and I have not seen any effect whatsoever.

I'm assuming there must be some kind of limit switch that tells the blower motor to shut off at a certain temperature, but I don't know where to locate that. I can get a model number of the furnace, but this is an upflow, 110K btu Dayton brand that was purchased from Granger. I think they still sell a similar model.

I've had the service guy out once, but he was of no help. I'm hoping just to find the part, and try to replace it myself. At several hundred dollars for a service call, I'm not impressed with the local guys knowledge.

Old 10-06-11, 04:25 PM
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Post the model of the furnace, which can be obtained from the rating plate in the burner compartment of the furnace.

Most furnaces these days have a time on the circuit board which control how long the fan operates after the burner shuts off.

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