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We have a Central Electric Furnace model # EB12B. It is paired with a heat pump. We noticed the issue when we were running the A/C this year and is has continued while running the heater.

When the heat pump comes on, the inside fan for the air handler/furnace will sometimes come on with no issues and other times will start, stop, start (often multiple times) before finally coming on and running as normal. At times, the start up issues are accompanied by a buzzing noise. On several occasions this summer it occurred in the middle of a run cycle (buzzing, fan cutting off/on/off/on).

The outside unit of the heat pump was replaced 2 years ago along with the interior A-coil. The HVAC techs checked the interior unit and said that the rest of it was in good condition.

When this issue started this year we contacted the same company who replaced the heat pump. They couldn't find anything wrong and of course the issue did not present itself while the tech was there and he didn't do a lot of testing. He stated that it he thought is was the thermostat.

The second company we called did more testing and replaced the run capacitor in the furnace. The unit was fine (based upon what I heard when I was home) for about 2 weeks and started doing the same thing again. At that time we turned the fan into ON mode instead of AUTO (unable to continue with service call fees with no fixes) and it ran fine that way until 12/29/19. At that time the fan went bad (cage separated from shaft, etc.).

A third company was called for service. They replaced the fan and checked everything else out based upon the previous issues. He found nothing but based upon the system responding immediately to the signals from the thermostat he did not feel that was the issue. The unit ran fine for about 2 weeks and has started with the same symptoms (occasional fan start/stop/start, etc. with the buzzing sometimes).

Please note that the system runs fine 90% or more of the time with no issues on startup. Can anyone help with this? Am I better trying to replace parts at this point or bit the bullet and replace the entire furnace (hate to do that with new A-coil and blower). What to try next? Our next thoughts go to the sequencer, the relay or limit switches. All help is appreciated!

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It sounds like the contactor, relay, for the fan is intermittently missing a beat. This is usually caused by pitted contacts that develop from normal use. Sometime they make contact, sometimes they don't. You can try cleaning the contacts with emery paper for a temp fix but replacing it is a simple task. Turn off all the power before doing anything.

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  • I agree it sounds like a contactor (relay) the run cap being bad can cause high starting current that may have damaged it. Buffing the contacts usually will work if there is enough left but replacement may be needed if it is a sealed unit. – Ed Beal Jan 22 at 16:36

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