climate control knob is turned to warm from cold, the air remains cold?

When the climate control knob is turned to warm from cold, the air remains cold. The air conditioner works fine. Air flow (face), (face and floor), (defrost), (defrost and floor) all work as expected. Recirculate and outside air work as expected. I surmise that the temperature actuator is the problem. If this is correct, then my problem is the location of the actuator. If not, then which actuator should I be at and where is it located. I forgot to mention that thermostat is good, input and output heater hoses are at after the engine warms up. Your assistance in this frustrating issue will be greatly appreciated.