I have all Carrier AC units in the house, and have been trying to connect a 24V AC smart thermostat to them.
What I discovered when this did not work, is that the that the AC control on the wall is a 5V DC wired remote.
Was wondering if anyone else has had the misfortune of having these AC units and found a way to replace the wired remote with a smart thermostat?
There are 4 wires connected to the wired remote (Red, Black, Yellow & Grey) which looks like the Red/Black is 5V Supply, and Yellow/Grey some serial communication.
Have you tried this?