The green wire connects to the fan.
Fan coil unit thermostat wiring.
This wire connects to your heat pump if applicable.
If fan speeds are adjustable the relay board is producing 24 volts.
I have further analyzed the wiring between the fan coil units and thermostats and it definitely looks like temporary stuff.
In the most basic system this functionality is provided by use of a fan center relay and the low voltage wiring to the thermostat now will require a minimum of three wires for heat only units and four wires for heat cool fan for control.
This additional terminal is labeled g in the thermostat.
The yellow wire connects to your compressor.
The white wire connects to your heat.
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Verify fan speed will change from high medium and low by utilizing remote 3 speed switch thermostat or connecting by p18 to p15 p18 to p16 or p18 to p17.