furnace fan not working properly

[xtreme6]

Hi there i have a nortron furnace it is about 1 year old and my fan is not working properly its cycling properly through the different speeds the weird thing is sometimes at the end of the cycle it shuts off for a second and then comes back on for a couple of seconds then off again and that doesnt sound very healthy when it does it. i phoned where i bought it but they didnt know anything about them you would think if you were selling them you would know something. does anyone have any suggestions and they would be appreciated.

[HayZee518]

check the fan's hi limit in the plenum. the on-off proportional may need adjusting. look for a box with a removable cover - 3"X1/2"X4 inches.

[xtreme6]

not sure what the plenum is and if i find the box how do i adjust it

[xtreme6]

Im looking in installation and operating instructions and the only limit it says is a automatic limit in the replacement parts catagory.

[HayZee518]

the plenum is the sheet metal box directly above the heat exchanger where your distributing ducting goes.

[Hube]

FYI, the high limit does not control the fan ,it controls the burner's operation only.
The fan control is most likely the culprit.
On some furnaces ,the fan control can be incorporated within the high limit but is a complete separate adjustment and has nothing to do with the high limit whatsoever.
A faulty fan "relay" can be another cause