heating control

need some help- My temperature gauge on my control panel will go from blue to red however it does not turn the heat on. When I turn in over to red the ac is still on. I replaced the front panel control section thinking the knob was messed up so it was not turning it to warm however that did not work- So I am wondering if anyone knows what my porblem could be. The temp is always cool no matter what the control is on.
Thanks

I'm having similar problems w/ mine but on the hot side! When I checked w/ the dealer (service mgr.) he indicated it was either the control (at the dash) or the gate mechanism (not sure of proper terminology) wasn't switching from hot to cold. This might be the same thing??? Not sure. My control module lit up like a Christmas tree recently so I'm hoping my control module is bad?!!?
Good Luck.