Carrier 38YDA036300 Heatpump continue to heat when satisfied

[scott38]

I am working on a carrier heatpump that continues to heat when thermostat is satisfied. This does not happen all the time. It works perfect for a few days and then it will stick and continue to heat. I have read that it possible could be the defrost board but did not know if anyone else had ran into this problem.

[HighlandThunder]

Are you saying that the entire heat system gets stuck? 1st stage heat WITH blower still energized as well?

-Brian

[scott38]

The thermostat satisfies. The outdoor unit still runs with the indoor blower running. I had the thermostat set on 65. Let it run and cycle 3 times. Shut off and came on exactly like it was suppose to. Left the job. Get a phone call a week later saying that it is 90 in the house. No one lives in the house currently so thermostat is left on 65 to keep some heat. Read a couple things that seem to point to the circuit board which has the defrost control built in to it causing this but i'm not 100% sure.

[HighlandThunder]

Okay, the thing is, without you actually being able to test the system during the malfunction it is just a guessing game until you do get to observe the malfunction. Now having stated the obvious, remember that the outdoor unit does not even have control over the blower circuit unless its defrost relay is sticking closed thus energizing the axillary heat which would cause the AHU to energize the blower, but this is most likely not occurring.

The more likely malfunction is a sticking axillary heat relay in the AHU or the rare sticking relay in a digital thermostat. I have only encountered on digital thermostat do this myself.

The best way to accurately diagnose these types of problems is have customer call if malfunction happens again and ask them to leave the thing as is if you can get there quickly so you can observe/test in the malfunctioning state. Once there, your volt meter is your friend. It will just be a matter of figuring out where the voltage to energize is coming from.

Good luck - these types of problem are a royal pain.

-Brian

[HighlandThunder]

Edit: 2nd paragraph: "I have only encountered this on a digital thermostat ONCE myself."

[scott38]

I have replaced the thermostat, the air handler curcuit board, the heat sequencer, the expansion valve, the flex return duct connecting the return. Obviously all these things were not because the heat sticking. I did however catch the unit doing this the first time i got called to this house and checked the circuit board in the air handler. Thats why that got changed. The flex was crushed from someone else, The other thermostat was changing indoor air temp readings sparactic so i changed and expansion valve was due to refrigerant readings. The only things left that i feel would affect this would be the circuit board in the condenser. Circuit board is very expensive so i will go out again to troubleshoot.

[dandyme]

what model a/h?

is the blower relay in the a/h control board or separate?

[scott38]

AHU model# FK4CNF003 Serial# 3398A31753
Condenser model# 38YDA036300 Serial# 3698E03671
Relay is on ahu control board.