2002 Dodge Caravan Heater blows hot, then cold

After engine warmup, when I turn my heater on, it blows very hot air, followed by a gradual cooling to nearly cold. If I turn it off for a few minutes and turn it back on, it again blows hot air, followed by gradual cooling.

I suspect the blend, a/c, or mode door actuator or the a/c heater control module. How can I test to find out which actuator, and how do I ensure the acuators are receiving the signal from the control module? Oh yeah, do I have to pull the dash to access the door actuators?

Also, any other ideas would be greatly appreciated.

Thanks for your help. Scott