I have 02 Blazer 4dr 4wd, The heat comes out of the dash vents all the time and it will come out of the floor or defrost if I shut all the dash vents. I took the bottom plastic off of the dash on the drivers side by the throttle and was watchin the actuators the move the blend doors and they move just not far enough, I can givethe top oneif i remeber righta little help and it will blow the heat out where its suppose to be. Does anybody know what would cause it to do that? thanks

 

just had this happen. there is a second actuater above the throttle pedal. mine looked like it moved but was sticking and not letting the floor or defrost work. figured out had this because there onr=e way vaccum chek went bad and got oil in the vaccum line
good luck

 

Check the vacuum hose to the vacuum cannister connection under the hood, on the drivers' side near the firewall. It may be disconnected and you are not getting enough vacuum to the a/c controller.

 

I had the same problem with the 2002 I got but it was under the dealer warranty still, the actuator valve had to be replaced because it was opening but not switching properly or something like that, seems like you may be on the right track.

 

I noticed there was some oil in the vacuum lines. Where is the vacuum canister located at?

 

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If you have oil in the vacuum lines I would recommend replacing the transfer case vacuum switch.

 

When you get the vaccum problem taken care of let us know if that fixed your problem!!!

 

maybe I should go find my glasses.........