I have a 2003 dodge ram 2500 ... when i bought it i had to remove the blend door thing, it was blocking my fan. Since i have noticed my heat does work. It will work a little and blow a small amount of heat, but then cold. My question is would my blend door cause my heat to malfunction like that, the blend door that works the inside outside air, or would it be the heater core... I dont know how the heater works. Does the heat draw only inside air or does it use outside air?