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I have a Daikin ductless heat pump with 3 heads. When the set temperature is reached, no heat comes out and the fan stops? Is the indoor fan supposed to stop after reaching the set temperature? I don't remember seeing this behavior when running on cooling mode this past summer.

Thanks.

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    Do you want it to continue to blow cool air around the house when the heating elements turn off?
    – FreeMan
    Nov 17 '20 at 22:56
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    The controls of the Daikin models I have are extremely inconsistent. Sometimes they will keep the fan on even in auto mode, and sometimes they won't even in on mode. I have the Wi-Fi control modules for my units and I'm writing my own software to control them.
    – Moshe Katz
    Nov 17 '20 at 23:54
  • Good point FreeMan. Maybe it doesn't make sense to make blow air when heating off. Thanks.
    – Z C
    Nov 18 '20 at 1:32
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I can't speak to this specific unit, but in general forced air HVAC systems have two modes for fan:

  • Auto = Fan runs whenever the heat or air conditioning is running - i.e., to circulate the hot or cold air

  • On = Fan runs all the time.

Most often I see "Auto". Occasionally people prefer "On", especially in the current pandemic as constantly circulating air means it passes through air filters more frequently. (On the other hand, most HVAC air filters aren't all that great and it also means you circulate the germs...so who knows what is best. As with so many other current "recommendations". But I digress.)

Arguably, fan "On" in cooling mode makes sense as circulating air, even if it is not "cold", helps you feel cooler. Same idea as ceiling fans, though less forceful.

Anecdote time:

I had a commercial customer (computer hardware/software, not HVAC). They got a new HVAC system with a fancy thermostat. They ran a nearly 24/7 operation, at least from 4:00am Monday to 6:00pm Friday - sales & accounting during the day, order processing/shipping through the night. They wanted the fan "On" all the time. The HVAC people tried but couldn't figure it out even though that was their job.

I read through the Chinglish manual and figured it out. The thermostat wanted to divide every day into "occupied" and "unoccupied" times. During the occupied times, fan On vs. Auto worked as desired. During the unoccupied times, the fan would always be in Auto mode. That actually made sense for a typical user - if you have substantial time where a building is unoccupied, it makes sense not to run the fan since nobody is there to appreciate the cooling effects (in the cooling season) and/or just not have the air feel "stale".

The solution: Set the unoccupied times to 2 15-minute intervals (e.g., 7:00pm - 7:15pm and 8:00pm - 8:15pm) and the rest of the time (23-1/2 hours a day) the fan would stay on as desired.

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