I have a two-story condo built in 1969 that has a Summer-Winter switch next to the main thermostat on the first story. The second thermostat is a heat only thermostat on the second floor. I would like to replace the old thermostats with digital thermostats, but want to make sure that the summer-heat switch will work with them properly. As I understand it, the summer-heat switch tells the thermostat whether to work as a heater or air conditioner. Is this correct? And will this switch work with new digital thermostats? I understand that the thermostat upstairs will have to be a heat only digital thermostat.