I have a 2001 dodge 1500 v8 5.2. I noticed today that my truck blows heat if the thermostat is pointing at the red(heat) even though the fan is turned off. It blows cold air when the thermostat is pointed at blue(air) and the fan is turned off. It really starts to blow hard once i hit 45-50 mph.

Any help would be great!!!

 

Normal. The heater gets its air from the cowl at the base of the windshield, when the truck is moving, that becomes a high pressure area, so, naturally, the air wants to go to a lower pressure area. Easiest way is into the cab.

 

Well then why does the air coming in my cab change temperature when i put it on hot or cold?

 

Because it is taking the same route that it normally would if it was being moved by the blower motor..... there is always some air flow....... (when the truck is moving.) the blower just moves it more enthusiastically.

 

yep...completely normal. All off does is turn of the blower motor.