Greetings again. I'm in need of a replacement for my 20 yr old thermostat indicated in the subject line. Mine is a 4-button model which I have been unable to find on the internet. Everything I've found is either digital or has 5 buttons. Neither of these indicate what thermostats they replace. Anyone know if the new digital models or the 5 button model is a replacement for the one I currently have? Mine is a 2-zone model. The buttons on mine are: fan, mode, up, down. It connects to the heater/air conditioner via what looks like a phone type jack.