I've read numerous threads on this model but could not find a solution. I just replaced my old thermostat with this model. The wiring on the old thermostat went as follows:

Red - Rc jumped to Rh
White - W
Green - G
Yellow - Y

When I removed the old thermostat I noticed there was a blue wire which was not connected to anything. When I put in the new model I wired it exactly like the old one but the fan (AC unit in backyard) does not turn on (on Cool/On mode) so the AC is not cool. (Gas Furnice)

Any help here is apreciated.

When I taped the red, yellow, and green wires together the ac worked. Does that mean the thermostat is defective?

You have it wired correctly, and connecting the wires as you did simulated the stat, so seems it is not working .

Turns out it does work when the stat is on "Cool/Auto" but not "Cool/On"... is that normal?