Mini split AC: indoor unit is off but still gets cold?

Hi. I just had a mini split AC system installed. One outdoor unit with 4 = indoor units. When I turn one indoor unit on to cool the room, I notice = that the other 3 (in 3 different rooms) also get cold (though their fans = are not on). Just curious: don't each of these operate like zone = valves? Seems wasteful to pump refrigerant through all when only some = are "on". Interested to learn, Theodore.

So with no air flow, do they freeze up? Just curious.

Yes. I observed the unused interior unit frosting up. Didn't become a solid mass, but this (and the sound of the refrigerant in the pipes) is what drew my attention to it when it was "off."

Yes units might show some frosting but there is another situation on multi evaporator's system. It is "critical charge". what happens when there is no load, Evaporators start freeze up some, at same time pressure drop and condenser looses must of liquid; results are Evaporator in use, starts to get partial liquid and partial cool gas feed. Be aware of that charge is very critical and you can flood compressor easily.

Yes. I observed the unused interior unit frosting up. Didn't become a solid mass, but this (and the sound of the refrigerant in the pipes) is what drew my attention to it when it was "off."