Bypassed both limits, no change. Blower never reaches full speed. Still has old style relay so no circuit board. Booster blower seems fine but has integrated centrifugal switch... does this control blower? Also, if I leave power off for half hour blower works but short cycles. Im at a total loss and its 18° and falling outside.

integrated centrifugal switch

That sounds like cut out switch for motor start winding.


Motor has two sets of windings, one to start, one to run. When motor gets up to speed, start winding is cut out (turned off) by centrifugal switch, motor then runs on run winding.

In other words motor is shot, defective run winding. Motor slows down and start winding reengages (at less than full speed). Not designed to run on start winding, eventually motor over heats and turns off until it cools.

That sounds like cut out switch for motor start winding.


Motor has two sets of windings, one to start, one to run. When motor gets up to speed, start winding is cut out (turned off) by centrifugal switch, motor then runs on run winding.

In other words motor is shot, defective run winding. Motor slows down and start winding reengages (at less than full speed). Not designed to run on start winding, eventually motor over heats and turns off until it cools.

Thx so much... I knew the booster blower had a centrifugal switch, wasn't aware the main blower did as well. Figured something was up when I couldn't find a capacitor... thanks again sir!

This is a common problem with Coleman mobile home furnaces. There is a bi-metal thermal switch which controls the fan. They are notorious for going bad & causing exactly the problem you describe.