[brownfoxx1]

Just had the heater core replaced.
Adjusting the location selector knob
Doesn't work. Only blown great heat thru the a/c vents.
But no airflow to defrost.
I replaced the control unit a month ago because it
Wouldn't low on high. New unit fixed that. So I swapped control unit just to see if it suddenly went bad. But still no defrost airflow

 

[rickaren]

Heat actuators

There are 3 door actuators on the HVAC system; Mode doors, Blend door, and Recirculation door. The 3 actuators are interchangeable.
Mode door controls where the air goes, Blend door controls temp, and Recirculation door controls outside air/inside air as the air source.
What you are describing sounds to be the Mode doors.

Fix on an actuator. If this is the case though and you must align flap gears your about to tear it back down. Pull the actuaors loose and set your controls to one specific level such as floor only or defrost only on full heat. This has to be done with it tore down but everything plugged in.

Here’s how. Consult the repair manual to identify which actuators control the defrost-vent-floor “mode door” and the temperature-regulating “blend door.” Then peer under the dash and locate the suspect actuator on the heater box.

Dodge Nitro Owners Help Info

hvac.pdf -- 2.2 meg