2003 Blazer, 4WD (3-button dash)

Hi all,

I'm starting to get a little cross-eyed about diagnosing my HVAC in my '03 Blazer LT 4WD (3-button dash). It seems to be operating in default mode, putting most of the air out the vents, and a little out the defrost and floor. Operating the mode switch has no effect.

I've torn the dash apart and have gotten to all 4 actuators. The air inlet valve actuator (fresh/recirc) is leaking, but the other three actuators are all holding a vacuum (I tested the actuators with a mity-vac to verify that they hold.) I removed the connector from behind the mode controller and blew all the lines out behind the dash. I got just the tiniest amount of vapor from the orange line (going to the air inlet actuator), but no other liquid from any other lines. There's no ATF pooling anywhere, and my transfer case was actually a little low (I've read about the vacuum actuator switch on the transfer case going bad).

I tried hooking my Mity-vac to the black line by the gas pedal (I assume that black is the vacuum supply?), but my little gadget can't seem to pull enough vacuum to make things work.

So now that I've been staring at this thing for too long, I'm starting to get a little brain addled. Do I need to start checking the vacuum lines under the hood, or is there anything else inside the cab that I need to look at first?

 

I always thought the default mode was defrost and floor, making me think something is hooked up wrong

 

Using the diagram at the bottom of this page, I've confirmed that all of the actuators are hooked up the same way as the diagram.

Actuator diagram

I bought the vehicle in 2006 and have had it ever since. I'm not aware that it was ever touched before then. Given that everything worked until a little while back (and that this is the first time I've ever had it apart), I'm inclined to think that everything was hooked up properly.