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HVAC Guru
HVAC Guru, HVAC TECH
Category: HVAC
Satisfied Customers: 14410
Experience:  15yrs in the HVAC industry with certificates and degrees.
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My interior unit/air handler is not shutting off. Replaced

Customer Question

Customer: My interior unit/air handler is not shutting off. Replaced the thermostat but did not solve the problem
JA: Thanks. Can you give me any more details about your issue?
Customer: Fan keeps running. Will not shut off unless I throw the breaker
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Submitted: 1 year ago.
Category: HVAC
Expert:  HVAC Guru replied 1 year ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset I am just one of the techs on here and I try to get to as many customers as I can and I just picked up your question now. Please give me time to respond sometimes I get your replies late so there may be a delay in my response.

Is the unit displaying or flashing any error codes on the board in the furnace or airhandler?

Customer: replied 1 year ago.
no codes or errors on the thermostat. Not sure where the board is located in the unit. I do have the covers off but do not see any displays of any kind
Expert:  HVAC Guru replied 1 year ago.

Ok is this a furnace or just an airhandler?

Customer: replied 1 year ago.
air handler. electric AC/heat pump. outside unit shuts off. air handler does not
Expert:  HVAC Guru replied 1 year ago.

It sounds like a thermal limit may have tripped and the unit has overheated then it will run the blower all the time, this may or may not be something you can repair depending on your electrical knowledge or skill level. Are you skilled?

Customer: replied 1 year ago.
pretty good at repairing things but have limited experience on this issue. Can you lead me through it?
Also when I started to trouble shoot it I did find that the condensate line was backing up and not draining properly. Could have activated the overflow shutoff switch. I have repaired the drain issue now. do i need to reset something?
Expert:  HVAC Guru replied 1 year ago.

Yes shut the power off to the unit for 1 full minute then turn it back on see if it all works again and let me know.

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Customer: replied 1 year ago.
I do not know if the issues are related. In other words if the constant running of unit caused the overflow or it was unrelated.
Expert:  HVAC Guru replied 1 year ago.

That would be related as it could cause the issue for sure.

Customer: replied 1 year ago.
i did have unit off for sometime when I replaced the thermostat and turned breaker back once thermostat was installed but still had same issue
Expert:  HVAC Guru replied 1 year ago.

Have you checked to see if any thermostat with a reset button in the unit was tripped? There are thermal rollouts in the unit that you should check.

Customer: replied 1 year ago.
I tried the reset button on the old thermostat before I replaced it but it did not help
Expert:  HVAC Guru replied 1 year ago.

There should be more than one.

Customer: replied 1 year ago.
I can turn the unit back on at the breaker again but need to put the cover back on real quick. Is there something I need to check in the handler unit itself before I put the covers back on?
Expert:  HVAC Guru replied 1 year ago.

No it should be where the heater is

Customer: replied 1 year ago.
more than one reset button in the thermostat?
Expert:  HVAC Guru replied 1 year ago.

No where the heater element is.

Customer: replied 1 year ago.
where is the heater located? it is a heat pump/AC unit
Expert:  HVAC Guru replied 1 year ago.

Do you have electric heaters? If so where they are.

Customer: replied 1 year ago.
I a sorry but do not understand the question. It is a heat pump/ AC unit. I see the coils, the Blower fan, and do not see any heating elements though
Expert:  HVAC Guru replied 1 year ago.

If you remove the G wire to the thermostat does the fan stop?

Customer: replied 1 year ago.
I will check, give me a minute
Expert:  HVAC Guru replied 1 year ago.

ok

Customer: replied 1 year ago.
ok. unit was off at breaker for about an hour. no reset button on the new thermostat. turned back on at breaker and unit comes on even though thermostat is turned off. I will try and disconnect the green wire now
Expert:  HVAC Guru replied 1 year ago.

ok

Customer: replied 1 year ago.
green wire disconnected...unit still running
Expert:  HVAC Guru replied 1 year ago.

Then you either have a safety device tripped or a stuck relay on the board.

Customer: replied 1 year ago.
what sefety device?
Customer: replied 1 year ago.
safety
Customer: replied 1 year ago.
I did find heating elements. No display or reset button there
Expert:  HVAC Guru replied 1 year ago.

It would be hard to say without seeing the wiring diagram

Customer: replied 1 year ago.
ok is there something that may need to be reset if the electric overflow switch was activated? Should that switch shut off the unit if it detects water backup and is tripped?
Customer: replied 1 year ago.
the unit was definitely backing up water and I cleaned out the drain and cleaned up the switch