If your house was built in the last 2-3 years, you probably have a "Hunter Pro-C Controller" Model PCC. Here's a link to the owners manual in PDF format. In the troubleshooting section, there is no readout that says "AC". (A "No AC" readout would be more likely, as others have mentioned above.) If it actually reads "No AC" and there is no loose or broken wire inside at the end of the power cord, could be the transformer that you're plugging in is bad. You've already verified that the outlet you're plugging into is good.
Unfortunately, changing the battery won't help.
http://www.hunterindustries.com/site.../om_pcc_en.pdf