Comment by akifbayram

From what I've read and experienced over the years, the indoor units of a Mitsubishi multi zone system never fully close their valves, so refrigerant flows through them even when they aren't actively heating or cooling. This becomes a problem when the indoor unit also runs the fan non-stop to get an accurate reading of the room temperature, since a thermostat with a remote temperature reading typically isn't available.

I got around this by disabling the fan from blowing when the indoor unit isn't actively calling for refrigerant. The refrigerant still flows through the indoor unit but since the fan isn't running, it isn't dumping conditioned air into the room. Every unit has a different way to disable the fan when it's not heating or cooling. My mini splits needed a jumper cut on the indoor control board but my air handler was configurable via a thermostat.

This raises the issue of getting a proper temperature reading of the room. Without the air flowing over the thermistor in the indoor unit, the reported indoor temperature becomes wildly inaccurate. To get around this, a thermostat with a temperature sensor is needed. Mitsubishi has a few off the shelf options. I went with the popular route of adding a Bluetooth sensor to my ESPHome builds and I sell a bundle including the controller and remote temperature sensor. More information here: https://serin-labs.com/controller/room-sensors.html