So I'm going to go pick up my truck from Cleveland next weekend and start driving it again since it didn't sell for me and I just remembered something. My heater only blow's cold air, and I have no idea why. Now I don't have the truck here to look at, and I can't remember if I put a thermostat in it or not last time I had the intake off. I probably did though, but if I did it's probably a fail-safe, so I can't rule that out, but I want some other ideas so I don't have to drive 400 miles in the cold if it's not that! So my ideas are these, if it's not the thermostat: I put the heater hoses on backwards, can you do that? Does it matter? I thought it didnt, but I've been wrong before. The other thing I have come up with is a guy at work said my vents and ducts are controlled by vacuum, and I may have lost a line, so the duct defaulted to open to the outside. Is this true? If so how do I fix it? thanks alot guy's.