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I have an electric furnace 240V. The blower motor starts then slows and sounds like it is laboring after about one second. It does start at full speed, however. Does the same thing when in constant on setting. There is a solid state time delay relay (on delay is 1 second off delay is 45), a blower relay, transformer but no control or logic board. I've verified 240VAC on load side of breaker. I've tested the elements and sequencer and they test normal. and I'm assuming the blower is ok as it starts at full speed then slows and it sounds labored while continuing to spin. Cycling power has no effect - starts full speed then slows. The timer relay is 24VAC. I'm unfamiliar with the characteristics so not sure what I'm looking for. I've narrowed it down, I think, to the timer relay, blower relay or, less likely, the transformer.

Any help would be appreciated.

Perry

  • What make and model is said furnace? Can you post the furnace's wiring diagram? – ThreePhaseEel Nov 1 '18 at 22:45
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I would be looking for a run/start capacitor it sounds like the start side is good but when it changes to run that one may be bad. Another thing is to lube the bearings there may be small ports in the front and back of the motor that you can drip some motor oil into, blowers don't require full torque until up to about 75% because they are not pushing much of a load until that point but a capacitor would be my first check unless you see the ports and have a oil can handy it only takes a few drops.

  • I agree that it sounds like a starting capacitor issue. Single phase motors need a capacitor to make them start spinning, then once they start it is no longer needed and is switched out of the circuit using what's called a "centrifugal switch" in the end of the motor which is closed (connected) at stand-still and opens at about 90% speed to take the capacitor out of the circuit. Your symptoms sound like the switch is not opening, it is stuck / welded closed. So once it gets to speed, the capacitor over-excites the motor windings and robs it of torque, while still consuming energy. – JRaef Nov 1 '18 at 22:48

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