Problem scenario
Your Carrier thermostat (e.g., a programmable Comfort (TM) Series Touch-n-Go (TM)) is not working. There is a glitch or apparent malfunction on the screen. All the lights flash on with the backlight turning on -- then the display goes dark (unlit with no indication). The heating and cooling does not work. The batteries seem good; the thermostat showed them at two-thirds strength (two of three bars were strong).
The display looks like this:
What should you do?
Possible Solution
Try with different known-good batteries. (This solution is particularly helpful if the thermostat itself is less than five years old.) The problem may seem like the original batteries are fine, but really they are defective. One Carrier thermostat manual (that comes with three different programmable thermostat models that Carrier makes) specifically say that the batteries should be replaced when there is one bar of strength left -- not when there are no bars of strength left. We recommend replacing the batteries as soon as the battery indicator light is visible that one bar of strength is gone/blank/weak and two are dark/strong. Otherwise you may have a problem as the one described above.
My wife and I experienced this for the first time last night since having a new system and this thermostat installed 8 years ago. We don’t have batteries installed and it has worked fine all these years. I removed the thermostat from it’s base, looked things over and replaced it. After the “ON” indicator flashed for awhile, everything returned to normal. I have no idea and internet searches have been no help.
Has everything returned to normal? Have you tried installing batteries for the first time to see if that helps?