I have what I guess is a package system, sort of. I have a pad mounted condensing unit outside with lines run to a package unit (rectangular wall-mounted with fan, coil and electric heat resistor strips all in one unit) inside. Right now my only options are to have the system running on Cool or Heat with either High or Low fan settings, no thermostat so it's either "ON" or "OFF." Is it possible to install a new thermostat somewhere within the current system to better regulate cooling when I'm not around, i.e. leave the system on cool but have the thermostat turn it on and off rather than having it run constantly?