here is an app that allows creating rules for temperature management. turning on a thermostat to cool or heat a house is already built-in to the app. but it does not currently handle a two stage solution like @bravenel described using evaporative cooler and heat pump or heat pump and gas heating in your case.
if you are interested in giving the app a try i would be happy to extend the app to support two conditional cooling/heating sources based on temperature (and power usage) range.
