I just installed a Honeywell RTH2300 in my home to replace an old mercury unit. It appears to be somewhat working, but the AC/Heat will not shut off. For example, it is set at 75 and the ac keeps running down indefinitely. Also, when the thermostat is switched to the 'off' position, the heating/ac unit keeps running and stays on.

I have read the owners manual and installation guide cover to cover and nothing seems to jump out as something I did wrong. Any help would be appreciated!