I installed a Honeywell RTHL3550D non programmable digital thermostat in my 5th Wheel Toy-Hauler . I went into the setup menu on the thermostat and turned on multistage cooling fan and connected the high sped fan wire to Y2. If the temp differential is high enough the fan runs in high speed, if the temp differential lowers enough the fan returns to low speed. In full auto mode, which also needs to be turned on in the setup menu, the thermostat will automatically go from heating mode to cooling mode and vise versa as necessary. In auto a 3 deg separation will be maintained between the heating and cooling set point. The next time I go to the RV I will get the wire assignments for the Honeywell and the setup menu changes as well and edit this post with the appropriate settings. This thermostat replaced a duotherm thermostat commonly installed in RV's.