The Genuine Comfort PTAC unit comes set up out of the box in display control mode. In the scenario an external 24-volt wall thermostat control wants to be used, use the following instructions to correctly switch the unit over. 

1. On standby off mode (the unit still has power but is not functioning), press the HEAT and the "+" button, holding down for 3 seconds.
2. The LED display will read a lowercase "r" to represent remote mode or 24-volt wall thermostat control. See Fig. 1.
3. The unit can now be controlled via the wired thermostat connections. 

NOTE: In "r" mode (24-volt wall thermostat control), the display buttons on the unit will have no control of the unit. Only the wall thermostat.  

To switch back to display control mode, repeat the same process.

1. On standby off mode (the unit still has power but is not functioning), press the HEAT and the "+" button, holding down for 3 seconds.
2. The LED display will read an uppercase"P" to represent the display control mode. See Fig. 1. 
3. The unit can now be controlled via the display.

Fig. 1

GCTW

The steps above will apply for GCTW units. However, instead of HEAT, your display will have an option for MODE. Holding down MODE and + for 3 seconds will switch the unit from display to remote and vice versa.