Intertherm furnace runs short cycles

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purchased a home about a year ago, it's got an older furnace (1981 Intertherm) and it's doing something strange. The furnace will light (hear the burner, feel the heat) the firebox will warm up, the burner will shut off, and then the fan will turn on.. The fan will run for a bit and then (I assume) once the firebox has cooled down the fan will stop, and the cycle will repeat until the house is warm. This seems not right to me.. Any suggestions on what to check? I did replace the thermostat with a round honeywell shortly after we moved into the home, and double checked my wiring job recently.

Now the furnace specs:
Brand: Intertherm
Model: MGH-055AB
Date Code: 81MY13N 01
Appliance Number: F000621171


From the controller board:
MAC 1165
MAC 1155

MG065
MG068

frompkin

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Hi,

Without being there, can't say for sure, but it is most likely a faulty Fan & Limit Control.

Thanks,
Robert