My setup:
I have three C&H brand 9k head units upstairs in 3 different rooms. One 18k slim duct unit downstairs. And a 48k compressor outside.

The scenario:
It's 50° outside.
The three 9k units have a set temp of 65°. The temp in the rooms is 70° and they are idle and aren't producing heat. The 18k unit is off and the room temp is reading 68°.

The issue:
If I turn the 18k unit on and up to 72° it starts producing heat but at the same time the 3 9k units also start producing heat and don't stop even after they all hit their respective set temps.

It's 76° and climbing in all of the 9k unit rooms even though their set temps are still 65°.

The same issue happens when using the head units as the thermostat or the remote as the thermostat.

The question:
Why is this happening?

  • @ Landoperk, IDKWYATA? Please use the full words to describe your issue. At least at the beginning of the question. Acronyms can be confusing.
    – RMDman
    Commented Sep 30, 2023 at 11:46
  • Should we assume you're talking about mini splits or soemthing?
    – Huesmann
    Commented Sep 30, 2023 at 13:00
  • Heat-pump tag, head unit, duct unit, compressor, C&H is a brand...
    – Landoperk
    Commented Sep 30, 2023 at 15:27
  • @Landoperk I edited that info directly into the question (where it belongs) because it was very confusing and it took time to find the info down here in the comments. You're free to edit your own questions/answers any time you'd like to add more details, clarifying info, etc.
    – FreeMan
    Commented Oct 5, 2023 at 15:25

1 Answer 1


The issue has been resolved.

Root cause
The culprit was a faulty management board on the compressor.

One of the terminals was throwing irregular voltages. The manufacturer said this could have been caused by a defect from the factory or an unregulated power surge.

Replaced the board.

Future Considerations
Installed surge protector at compressor unit.

  • 1
    Great news! Thanks for coming back to post your solution. So many people can't be bothered... :(
    – FreeMan
    Commented Oct 5, 2023 at 15:26
  • Indeed. Please take the tour, then accept your answer to resolve this question.
    – isherwood
    Commented Oct 5, 2023 at 15:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.