I have a 2014 lonestar with Cummins isx power. Lately I have been having problems with my HVAC system. I have had to keep moving the blending disk more and more to the hot end to get heat (when I did, I got great heat), now I have it full on heat and unless I engage the ac on max (which limits outside air if I remember correctly), I don’t get any heat into the cabin at all. Is the problem in the blending of the air or do I need to be looking some place else. Please help.
Sounds like the temp blend door or actuator, or the heater control valve. There is a valve on the coolant lines running to the heater core that is electronically controlled by the module on the dash. Have someone else turn the dial and watch the arm of the valve if it has full 90 degree movement I'd suspect the blend door or actuator.
Make sure the engine is hot like normal also. Sometimes in really cold temps or if the engine thermostat are wide open your engine coolant will show cold on the dash. Then you won't have any heat in the truck.
The Heater control valve is on the passenger side of the engine compartment, near the fire wall. The blend door and actuator for temp will be behind the passenger side kick panels near the door or firewall.
