Heat A/C control problem

I have a problem with my 99 Lumina's heat control. The heat/cool and fan speed switches work but it is stuck on defrost or blend and the A/C won't work right. I have tried swapping the heater control module with one from a junk car and have the same problem. I have also checked the fuses as best I can in the dash and under the hood.

Is there another module under the dash that ultimately controls the vent doors and A/C? The A/C appears to be topped off (it was actually high and had to be bled off a bit) but I can't get anything but the heat defrost to work. Any help will be greatly appreciated.