So the question is really in the title.

My carrier air handlers fan will not shut off. I have done the following:

  1. checked to make sure the fan was not set to on via the nest t stat.
  2. pulled nest off the wall to see if the fan stopped, it didn’t
  3. changed the only relay inside the air handler unit which was a T92P7F22-28 (I had tested the old one and it seemed to be functioning fine but at $10 why not).
  4. Pulled the plug from the fan motor and put a lead to my multi meter at C and tested the leads marked N and L with the other end of the multi meter and read 120ish volts on each, so I assumed that means constant 240ish volts is being supplied to the fan motor.
  5. breaker at the panel and of course breaker at the air handler unit will indeed finally kill power
  6. ac condenser outside works fine, nest shuts it off when desired temperature is hit but fan never stops.
  7. for kicks I got another nest, hooked it up, same issue
  8. replaced the nest base that it snaps into on the wall, same issue
  9. I also tested the fuse inside with the multimeter and visually it didn’t look fried, and the multimeter confirmed this.

I am somewhat out of ideas. There’s very few components inside the air handler it appears and anything else modular looking just seems to be related to the electric heater inside of it. I am going to attach pics if they help.

Air handler model: FX4DNB or FXDNF

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  • Can you post the wiring diagram for your air handler please? Dec 15, 2020 at 2:48
  • @ThreePhaseEel Thanks for the comment. Added more photos. Hopefully they help. I also added a photos from the manual that more or less matches the setup here.
    – MZawg
    Dec 15, 2020 at 2:53
  • Added model number from manual as well.
    – MZawg
    Dec 15, 2020 at 2:54
  • IF you disconnect the blue and white wires from the blower motor, does the blower still run? Dec 15, 2020 at 3:06
  • @ThreePhaseEel correct it will still start up when given power even with the speed leads removed.
    – MZawg
    Dec 15, 2020 at 3:08

1 Answer 1


I'd replace the blower motor at this point

It sounds like the blower motor has an internal short in it that's causing it to run even in the absence of a speed command from the air handler control circuits. I'd replace it with an OEM replacement part, as it appears to be some sort of module with an internal speed controller.

  • Thank you for the answer. Any good way to test that to have any sort of verification?
    – MZawg
    Dec 15, 2020 at 5:09
  • @MZawg -- I suppose you could double check a service manual for your air handler if you can find one? Dec 15, 2020 at 5:11
  • Will do. Finally, just on a quick browse. The rear of the motor says endura fm19. Looking at search results coming back I see parts that are just that rear assembly. Since the motor spins, perhaps replacing that control module might be sufficient? Thoughts?
    – MZawg
    Dec 15, 2020 at 5:17
  • And then to add just a little more to that. Should the 4 wire white connector (not the wires going into the speed plugs), read 120v from two of the contacts at all times?
    – MZawg
    Dec 15, 2020 at 5:18
  • @MZawg -- it should read 240V between the L and N terminals at all times, yes Dec 15, 2020 at 5:19

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