howdy all
just yesterday i noticed that no matter what mode i select for HVAC, (defrost, mix, floor, etc) the air comes out in all three places. any quick suggestions as to whether it could be a vacuum problems, an electrical problem, fuse problem or what. fan speed and temp selection work fine. years ago it was a vacuum problem or mechical linkage, but not too sure with today's sophistcated technology.

 

I really hate to tell u this, but you have a common (and expensive) problem. Your HVAC vacuum components have been contaminated with Automatic Transmission Fluid. This is caused by an overheated transfer case, i'll explain.......when the t-case gets too hot pressure builds up in the case and it causes fluid to be sucked into the vacuum switch on the t-case that controls the front axle diaphram. It then in-turn gets into the vacuum resevior and eventually makes it's way to the hvac vacuum harness. ATF speads soo thin that 1 drop of it will practically coverthe entire hvac system. Now the parts aren't too expensive, probably $200.00-$300.00 for all of them, but you do have to remove the dash to replace them. It's been my experience that ALL HVAC VACUUM components will have to be replaced in addition to the vacuum resevior, the t-case switch, and the vacuum hoses if possible. I usually spray some parts washer into the hoses with both ends disconnected and then spray compressed air through them (repeat several times) and reuse the hoses.
The easiest way to tell if this is your problem (I am positive it is since I have only seen this ocurr on 2003 MY's and I have fixed at least 6 of them) is to look at the vacuum supply line where it comes out of the body harness right beside the gas pedal, there is a clear union there where it connects to the dash harness (vacuum) the clear union will look like it is red or brown depending on the condition of the ATF. And you can seperate it and see/fell the ATF. Again sorry to be the bearer of bad news.
Here is a parts list:

HVAC control head
t-case switch
vacuum tank (on the insde of the left front fender behind the ABS BPMV and EBCM)
HVAC upper mode valve actuator
HVAC defrost actuator
HVAC air inlet actuator
HVAC recirculation actuator
HVAC vacuum harness 1 (mounts to the case and connects to all 4 actuators)
HVAC vacuum harness 2 (Connects the Control head switch to the other vacuum harness)

 

whoa! oh my goodness. i certainly wasn't expecting it to be a problem like that. but i do appreciate your quick and thorough response and at least i know where to begin. however what do i need to look for as far as the trans case overheating. i did have to use the 4x4 the other day in bad weather and the timing of the havc problems seem to correlate to the last couple of days.
laser