I have this Honeywell RTHL2410C programmable thermostat and typical Florida electric AC system. Starting this Spring, it has started behaving strangely when switching from Heat to Cool mode.
The thermostat has a physical switch to change the mode (or to turn it off completely) and separate programs for the two modes. When I move it from heat to cool, the thermostate becomes partially unresponsive for quite a long time (at least 30 minutes or more). During this time, the unit does not turn on and I can't set the temperature override or do anything to coax it to turn on. The thermostat has power; it's backlight comes on in response to pushing the buttons, and I can even adjust the programming, set the time/date, switch the fan from Auto to On, etc. But I can't adjust the temp or use the Run or Hold buttons. It's like the thing is actually in Off mode although it's definitely in the Cool position.
The past 2 times this has happened, the unit eventually "woke up" and came on and cooled as expected.
Also, the unit is not running when I switch the mode; for example, today it was quite warm when I got home and switched from Heat to Cool, so the unit had not been on since early morning.
This only recently started happening; in the past it's worked as intended when changing over from one mode to the other.
It doesn't seem like the thermostat is faulty, since it mostly works. Could it be a partial fault? Any ideas for troubleshooting are welcomed.
Best Answer
Based on the installation instructions for the model you listed, you have two AAA batteries. I recommend you begin by replacing them.