Hi there. Hope anyone could help.

I have this control for six years. Today I got home and it showed "low battery" sign. Apparently the power went off for awhile as the clocks were all messed up.
I changed batteries (2 "AA" size), even it is optional according to the mannual. However, the "Battery low" sign stays on. I then disconnected all the wires and re-connected. It still has the "Battery low" sign on LED.

Can anyone tell me if the thermostats is not working or the airconditioner is damaged?

Thanks

Thermostats of this type,as u stated,have an optional battery capability.The batteries power the thermostat if the furnace is not powering it.If the thermostat is being powered by the furnace(best way)then there will be a "C" terminal with a wire connected to it.This is the common terminal off of the furnace transformer.The "R" terminal is the hot terminal for power as well as the switched leg for the relays and contactors in the system.The problem most of the time is that if a homeowner upgrades the tstat or it is installed by a so-called professional,the wire is not replaced.The wire normally used is a 4 conductor,which means it has only 4 wires in it.One for R,G,Y and W.Those terminals are necessary for operation of the fan ,cooling and heat,which leaves no common for the thermostat,therefor leaving the batteries to power it all the time.If the batteries die in this senario,your AC dies.Ideally,the thermostat would only use the batteries when the power goes out to keep time and date current until power is restored.If u replaced the batteries with new batteries and it still displays batteries low,i would try cleaning the battery terminals and rolling the batteries around to make sure u have a good connection.If it continues to show up,only other option is to replace thermostat.Usually it is good practice to replace the batteries @ least yearly in a tstat that is powered all the time by them.Hope this helps.

Thanks BasPro!
I almost gave up and this morning I decided to try one more time. I did disconnect all wires as well as batteries. I left it alone for a few minutes. Then, I opened up the panel and basically did nothing other than shake and clean the dust. When I put everything back togeter with an other set of battery. Well, the error message of "Battery low" is gone. Obviously, I lost all programm. I re-connected wires and everything works.

I guess it has some type of capacitor inside which it can last a few minutes without power. So, it has been totally reset.

I did save $100 for a new one.

Thanks for your reply.

So, I took my T813C1012 off to paint...I put it back on and now the furnace won't work. I get sporatic low battery (even then I shouldn't need it as I have a common line coming in to power it). I check my furnace and it's giving me an error about the 24v fuse being open.

The Thermostat works with on batteries in and when set at Fan Auto the green power LED is on. However if I switch to Fan On, the green LED goes off. The System setting (cool, off, heat) doesn't affect anything and regardless of the setting in the console the heat/cool/fan does not come on.

HELP!!! All I did was unplug everything and change the batteries...now it doesn't work with or without batteries.

What must have happened is that when u took the tstat off the wall,u touched the red(R)wire against the common (C) terminal causing the fuse to blow in the furnace section.It should be no big deal as long as the fuse caught it.Probably a little 5 amp car fuse or a 3 to 5 amp glass fuse in the furnace section.Should be a control board mounted to the blower housing,the fuse will be on there.Get the exact fuse and replace it.5 amp car fuse @ autozone and 5 amp glass @ home depot.Make sure all fuse specs are the same,will probably be a fast acting fuse(which will be stated on fuse).Fuse could also be in series with wiring off control transformer going to board plug.Just look around,youll find it.Ususlly whenever i take a tstat off the wall,ill either unplug the furnace or pull the r wire off first and wrap some electrical tape around it.Good luck.

BTW,Unplug the furnace b4 u start messing around in the blower section,would always rather be safe than sorry,even if u have no control power.