I recently changed out my old mercury thermostat to a Honeywell RTH3100C digital non-programmable thermostat.

The issue I'm having is that once the desired temperature is reached on the thermostat the a/c won't shut off. What could be the issue?:(

Did this problem start as soon as you put in the new thermostat? If so you probably have a wire in the wrong place.Tell us how you wired the new stat and we will try to help.

If the problem started after changing the thermostat out, you have it wired wrong or programed wrong. If the problem was before changing out the t-stat, you got problems with the equipment. Like letmetellu said if you can give us more info it will help us. We promise not to bite.

We promise not to bite.You're no fun anymore... :p

The original t-stat was wired as such:
Y - Yellow wire
G - Green Wire
R- Red Wire
O - Orange Wire
W2 - White Wire
E - Black Wire
C - Blue Wire

This is exactly the way I wired my new Honeywell t-stat. The new one I bought has 9 wiring section whereas my old one only as 7 so the only two on the new t-stat that don't have a wire running to it is the "B" section and "L". Please help

Sounds like the new t-stat isn't multi-stage, so we'll throw that idea out... did you check the installation instructions for additional setup options? Maybe something isn't configured correctly. The "B" and "L" terminals are likely not needed for your system. Try this: set the system selector to "OFF" and the fan selector to "ON". Feel the air blowing from the registers - is it "room temperature" or does it feel "lukewarm"? Perhaps your auxiliary heater is powered for some reason...