After driving 3-4 hours at high speed continuous, the air flow for my heating and air shuts down. You can hear the fan running but there is no air coming out of the vents. What could the problem be? Is it the selector switch? because when I shut off the ac you can hear all the vents opening.

 

Did they just switch to the defrost vents, or, are you not getting any airflow at all.

 

No the air flow just shuts down. it is like all of the flaps are shutting off

 

Vacuum or electric powered actuators? Running the a/c? Not just the evaporator core freezing up is it?

 

Sounds like the evaporator core may be freezing up, which can be caused by a few things, including a clogged core (years of dust/dirt flowing through it and becoming trapped), low refrigerant pressure, or both combined. May not hurt to have the refrigerant pressures checked by a qualified mechanic.

 

3rd-Gen Dakotas use only electric-powered actuators.

 

Actually I changed the control board for the actuator motors. It was heating up and driving all the actuators to the closed position, hence blocking all the air flow.

 

these trucks have a shut off when you give truck power the acc. will shut down not to drain power from engine, nothing wrong with system just a simple shut off to not rob power.