I have a Honeywell thermostat which is prgrammable for weekday (wake, leave, return sleep) and weekend ( wake, sleep) cycles. The thermostat is mounted at normal height above a return. The wall does not get direct sun and there are no electrical appliance venting hot air near it. I don't know if there is a return running vertically through the wall cavity where the thermostat is mounted, but I can check... Warm return air from the upstairs rooms heatign up the wall where the thermostat is mounted may explain some of the following...
Recently I've notice the following behaviours:
1) The system will shut off during the cool cycle sometimes 3 or 4 degrees before reaching the set point. The little "Cool" display on the LCD disappears, so it's like the thermostat stops calling for cool rather than some kind of safety/thermal cutout. 3-4 minutes later it'll show "Cool" again and the AC will fire up again an continue trying to reach the setpoint.
2) When the thermostat is already at the setpoint (74deg) it'll call for cool every few minutes even though the temp has not risen. The AC will run for about 2 mins then shut off. Does this every ten minutes or so, off and on.
3) I can look at the thermostat displaying 74, and then 30 secs later it will show 76, then another 30 seconds later it will show 74 again.
I think the thermostat is either being affected by warm air from something near it, or the thermostat is just bad. It incorrectly senses the temp too low for a moment and thinks it's reached thesetpoint/stops calling for cool, or it incorrectly senses the temp too high and calls for cool.
Are these behaviours normal, or should I look at having the thermostat replaced?