The green wire connects to the fan.
Fan coil unit thermostat wiring.
The yellow wire connects to your compressor.
I have further analyzed the wiring between the fan coil units and thermostats and it definitely looks like temporary stuff.
To install your unit you ll need to connect the correct wires to the terminals on the back of your new thermostat.
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.
Here is the industry standard thermostat wire color code used for most systems.
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.
I am especially concerned about possible confusion between the fancoil s c terminal fancoil to water control valve and y terminal thermostat to fancoil for water control valve.
If fan speeds are adjustable the relay board is producing 24 volts.
This wire connects to your heat pump if applicable.