Hey, a while back the clips on my air recirculation vent under the dash broke so I just ripped it out and didn't replace it. Whenever my engine is at operating temperature, my heat only blows hot when my RPMs are above 1,800. If it is just idling at operating temperature and my heat is on it blows ice cold. Does that door have anything to do with it?

 

What year is your truck?

 

 

Check coolant level. It's acting like its low.