we usually have our a/c set to 72. the thermostat, on it's own will arbitrarily reset the temp to 84 or 85 degrees. we will reset and then it can happen again, 2 hours later. very sporadic. we thought maybe there was a battery to change, but couldn't find any batteries in the thermostat to change. sometimes it will work fine for 3 weeks, and then suddenly we will have to constantly reset the temp up to 5 times a day for 2 or 3 days,