Hey everybody,
I have a 98 blazer that I bought about a two years ago. I had it for about 3 months and I didn't notice anything wrong with it. Since I live in Wisconsin and I bought this in November and I didn't notice that my heat will not turn off. Its like the heat controls don't work I can turn it all the way into the cool and it still blows extremely hot air. The blower **** works so I can turn it off but it still blows hot air lightly even when the **** says off. I replaced my thermostat and I took apart my dash and made sure the control wires were all plugged in. I have no idea what it could be maybe the heater core? or maybe the controls on the inside? To fix it for the summer I put a valve on the hot water line and when I have it so there is no hot water running it will blow cold ac. Any advice would be great because I have no idea what else it could be and this is a pretty annoying problem. Thanks for reading!

 

Sounds like a blend door not closing. I believe the doors are vacuum operated. So check for vacuum leaks, etc.

 

The temp door is controlled by an electronic actuator. There are a number of threads about this including how to remove it.