I've been having the same problems as many people on the forum...it seems to be a regular issue. My system only blows out hot air. It seems to be the blend door actuator as I have been reading. I got a new one online, and started reading up how to replace it, it doesn't seem to be too big a deal even for a non mechanic like me. As I was looking behind the glove compartment, I noticed that there is a vacuum controlled actuator with a metal arm that looks like it is supposed to be connected to a white device sticking out of the heater system (like that description?). The metal arm is broken off of the white part. I'm attaching a picture I found if it online while doing some research...THIS IS NOT MY SYSTEM. My questions are, what does this piece do? Is this why I blow out hot air, and not the blend door actuator? Is their an easy way to fix it? It looks like I may need to tear apart the entire dash, but if it won't fix the heat problem, I'm not going to bother with it.

 

What year is the vehicle, and does it have manual HVAC or automatic climate control?