Why would a 2002 Chevy Blazer heater only blow cold air?

Answer 1

A. The Heat control valve (If Equipped with it) is Frozen in the closed position or the Vacuum line is not getting Vacuum to open it or if it is cable controlled the cable is not moving. B. The heater core is plagued with junk, you can check this by removing the hoses to it and connecting a water hose from your house to it to see if water flows through it. If NO FLOW try reversing the hoses and see if you get flow with a lot of junk in it to start. You could blow the Heater core and that is expensive BUT if no flow and there is no control valve in line that is closed you are going to have to replace the heater core anyhow. I replaced the one in my 1994 S15 4X4 Blazer 2 years ago and it took me (2) TWO Weeks to do it working on it every hour available as I had to pull the ENTIRE DASH out and replace it to get to the core! (Replacing the dash was far worse than removing it. I ended up with a BFH to do it.) C. You could have a Vacuum operated door that is not opening. D. Those are the CHEAP answers ROFL! IF you have a digital temperature control you could have a $$$$$$$$ Computer out! May I say that I hope you have a simple broken vacuum line but I would not bet on it. Keep your cool and remember (If it doesn't fit get a BFH to put it in place! ) Adrian