I have a York split A/C unit in a condo located in Mexico. I tried to change a mechanical coil type temperature thermostat to a digital type, spending hours to get it to work. I finally realized that the only two wires that were actually hot from the air handler to the mechanical thermostat were 120v and not the 24v that the digital called for.

No more wires can be pulled to the thermostat area as the run is very long from the airhandler to the thermostat and all wires are embedded in walls of concrete.

If I make the change-over, please advise the steps that need to be taken as the stepdown transformer appears to be too simple as the only step.

Thank you,
Rich