I currently rent out a home I own in IL and live in IN. The renter called and stated that they had to switch the thermostat from auto to on to cool down the house. Could this be a battery that is dying and not tripping a switch to turn the fan on? I couldn't tell you the last time I changed that battery, its probably 3-4 years old at least. That is just the first thing the came to mind. Any thoughts?