Where is the blend door located on a 1999 Chevy Blazer and how do you get to it?

Answer 1

The good news is that the entire system of several (it turns out) blend doors can be found in the clean and somewhat convenient interior under the dash board. The bad news is that you will have to disassemble the entire dash and center console to get to it. Keep reminding yourself that the pros may be quicker, but they will charge $60 to $90 per hour to do precisely the same thing you can do with hand tools and a power screw driver with the appropriate-size socket head.

Go about the disassembly carefully and as you snap the panels apart, if you feel too much resistance don't force it -- look for a screw you have not seen or another panel which must be removed first. And for heaven's sake, as the screws come out replace them for safe keeping in the framework holes they came out of. Otherwise, of the 30 or more screws of different lengths you'll be removing, some will end up lost, installed in the wrong places, or left over when your are done. (Horrors!)

[SIDEBAR: I take the Haynes Manual airbag warnings seriously. Before you start poking around under the dash with a screwdriver, take out the airbag fuse. They call it "Supplemental Inflatable Restraint" or SIR in the owner's manual and on the door of the fuse box. And disconnect the negative terminal of the battery except when you are testing the switches, etc., or you may short-out something you'll have to go back in to find later.]

I found two vacuum-actuated blend doors behind the glove compartment. I determined that the one on the left operates a door which switches air from the dash vent level to the floor level, and the one on the right redirects air from enclosed interior circulation to open circulation including exterior air. I discovered this by disconnecting each line in turn from its actuator and altering switch positions until I felt a distinct suction on my finger covering the open end of the line. It helped to moisten my finger a bit. I moved the switch to stop the suction then reconnected the line, reset the switch and watched the actuator to see that it responded to the vacuum.

Neither of these functions seems to govern the problem in my case. My air is blowing hot (not just low-refrigerant-level warm) regardless of the setting on the control module. The counter guy at AutoZone (we should be on first-name basis by now) gave me a few pointers on the theory and function of blend doors. It seems that there is a default position for at least the hot/cold door. A spring returns that door to the heater function until a vacuum through the line draws the door, closing the hot flow and opening the cold flow in the same motion. A stuck or nonfunctioning hot/cold door will cause pure hot air to blow even when the control is set to A/C and refrigerant is topped-off.

So far it was clear that the suspect hot/cold blend door actuator must not be one of the two I had found, so I traced the vacuum lines and found a vacuum distribution block located just below the heater/ac control module and behind the ash tray. It has five color-coded vacuum lines running from it, three of which run to the left toward the steering column. Of these, two lead to a single actuator above and to the right of the accelerator pedal. [I was just closing in for the kill when I ran out of time.]

Since this actuator appears harder to get at, I intend to disconnect the two lines one at a time from the vacuum block and vary the control settings as before, feeling at the posts for suction to confirm that this actuator controls the hot/cold door. If I cannot get vacuum at the posts, the vacuum block may be faulty. If I get vacuum at the posts I'll check the vacuum at the actuator end of the line. Absent suction there, the line is blocked; if there is vacuum there, the actuator is faulty or the blend door is obstructed.

My time is my tuition, but I am already paying myself what I would have had to pay a pro to do the same search pattern.

Ain't the internet grand?