AC Unit Hums when Turned Off, have to Flip The Breaker

Updated 05/15/2025 | Published 05/14/2025

Question:

I just installed an Advent ACCAR150 to replace an old Carrier unit. Both units hum after they kick off and the only way to shut them down is to flip the breaker. Any ideas what is causing it? Seems like since the old one and new one are doing it that it might not be the actual unit. Thanks

asked by: Chris B

Expert Reply:

Hi Chris,

Since you're noticing the same humming issue with both the new Advent ACCAR150 and your old Carrier unit, it’s very likely that the problem isn’t with the AC units themselves, but with a shared component that was reused during the install like the thermostat wiring, a control board, or a relay module in the ceiling assembly. Did you reuse any of these components when switching out the AC units?

If something like a relay or control board isn’t fully shutting off, it could still be sending power to part of the system, which would explain the hum and the need to flip the breaker. Let me know what kind of thermostat setup you have and I can help you dig a little deeper!

expert reply by: Heather A

Chris B.

5/15/2025

I did reuse all the components except the actual roof unit. Our unit is controlled by a remote. Thanks

Chris B.

5/15/2025

Would a bad freeze sensor cause it to do that?

Heather A.

5/15/2025

@ChrisB I don't think it would be the freeze sensor because the evaporator coil would be frozen, also this was happening with your last unit as well. The likely culprit is the thermostat since you are not using an air distribution box. I reached out to Advent to see what they think. Are you still using the ceiling assembly from the Carrier unit?

Chris B.

5/15/2025

I am still using the ceiling assembly from the old Carrier.

Chris B.

5/15/2025

And it does have the old air distribution box on it still.