I honestly do not hink that you need to pull the whole dash panel...since its so large, there are access points to just about everything. Schrade is right about one thing....it IS scarey in there. There are several mounting bolts and/or nuts, but I am not sure about those rivets. I do not think they hold the dash section in place. Just pieces of the dash together if anything.
The vac lines are easy if you know what to look for.
The main line under hood comes off the rear of the plenum to a small check valve with a T right between the distributer and the plenum. That vac hose runs to the firewall where it enters to the cabin.
Inside, it should enter somewhere high passenger side, near the center. From there there will be a couple yellow or orange (some kind of hard line) that runs all the way across the lower dash to the A/C programmer that is mounted just over the gas pedal. From there, the programmer distributes vac lines to the various vent doors. It can be seen in the photos.
The programmer has to be mounted right or it tends not to operate well. It likes to be tight and mounted flat, not cocked to one side or the other. Don;t know why,. but I've seen this a couple times where it would not work until leveled.
Make sure the elect plug is on tight, and check the vac fitting cluster. The control head sends signals to the programmer that operates all the vents. It also is part of the a/c compressor command loop,. so it has to be functional. Its one of 3 control components for the elec a/c system (opt 68).
Usually, a dead vent system defaults the air flow thru the defrost. If you get vents but no def, or floor, that smells like a bad or stuck vent pot. ALSO< the system is very precise in its programming....you may have t o run the temp up and down while set on "heat" or defrost in order for anything to happen. A cold temp number and a heat button almost send air no-where....a hi temp setting thru vents will end up in defrost or floor.
Temp set to 60 over-rides mix and goes to full cold. Same for 90 setting...no mix, all hot air thru the appropiate route, floor and some vent. Any temp set between 60 and 90 will allow the system to blend air and direct where alot of it goes.
Next would be to see if you had Vac at the programmer. if so, then the programmer may be at fault or the vent vac servos may be frozen in place. You CAN look directly thru the center vents to the door that MUST operate at the defroster to get any air to go to other vents. Look in there by removing the center bezel,. and watching as you change from 60 degree auto to defrost and heat. You should see it try to move. If not, then back to tracing the vac source.
You can also access the cross dash hard vac line from behind the stereo and a/c control head. They run with the harness and are bundled together with wires. Look for a hard plastic line thats yellow and about the size of 10 or 12 gauge wire.
You can also try to pull a vac on the main vac line by the plenum to see if it will hold or if it leaks from a break inside the cabin. Because it gets its vac directly from the plenum, there should be no obstruction between the fitting and the firewall unless the vac hose is kinked. The ck valve T needs to be there so fuel fumes cannot enter the cabin thru the vac line.
Another thought, The T under hood,. has 2 lines that go off it...one to the cabin for vent control and the other for the cruise control,. If your cruise line is bad or leaking air, thats part of the vac line to the inside, so that line needs to be fixed too.
hnoes
