1986E with electronic temp control.
When I got the car, it did not blast out the A/C vents, but just everywhere.
I put an aluminum clip in the left defroster vacuum motor to hold it shut, and the airflow through the vents doubled, but it still goes out the bottom "knee" vents too.

I was told it was the programmer, so I got a used one from the wrecking yard, and put it in, and no change.
Through the years, I played with it a little at a time, and never made any progress.
I think the vacuum to the heater valve is broken somewhere in the harness because it never gets vacuum. That vacuum line is in the harness loop that droops near the starter.
I took off the lower valance panels, and checked the double vacuum connector under the ECM, and it has vacuum. When I disconnect the orange hose on the in/out door, it moves.
So, my conclusion,
The programmer gets vacuum, the in/out door gets vacuum, and the controller has no blinking lights. I disconnected the programmer, and checked for the blink, and it is there. Reconnect, and it goes away.

I was poking around in the programmer, and mapped out the vacuum hoses, and then mapped them out on the car connector, and the pink and blue hoses were opposite between the programmer and the vacuum hose block that fits on the programmer. I removed the programmer, and swapped the pink and blue hoses internally.
No change.
The air is selected cold, and the air comes out cold.
The heater valve is wired shut for the summer.
(it's always summer here)
I wonder if the broken heater vacuum is bleeding off enough vacuum that the rest of the vacuum motors don't work.... but inside/outside valve works, so I'm guessing the vacuum is alive and well.
I have an FSM, but the FSM shows 5 solenoids, but I have 6, Also, the FSM shows 2 vacuum sources, but I have 1.
Not lost on this, but it is just so hot that I'd like a short cut about now.
Last week it was 117 degrees for 5 straight days. That means it was 121 in my garage during the day and 105 at night.

 

A little information to keep you in the house reading (where it's cool):

http://forums.corvetteforum.com/c4-t...schematic.html

http://forums.corvetteforum.com/c4-t...stic-mode.html

A friend of mine used to live in Ahwatukee. He told me that one Saturday morning he went to work on his car and the engine was still so hot from the day before that he couldn't touch it. I've spent a lot of hours sweating at Firebird while autocrossing on Labor Day weekend...

 

Did you test each solenoid to see if they will hold a vacuum? You might also check the tank, though if it were broken, cruise would be erratic and air flow would probably default to defrost on acceleration.

The Vette's a/c does bleed a little though the heat and defrost vents with a/c to cool the floor and keep the windshield clear. At startup, there is also a brief purge function - mostly floor - so it doesn't fog the windshield.

Assuming you have vacuum to the Programmer and the Solenoids are good, the main reason it isn't working is because it isn't getting a signal from the Controls to switch to something else (since you've tried another Programmer, I'll assume it's good). Other causes would be broken linkage or doors inside of the ductwork. You can usually disconnect or remove a solenoid to manually move the doors and I see that you've allready shut the defroster down.

 

The heater as well.
I see some people have blue boards, green boards, and white boards. I wonder if there are different revisions that are signified by different colors.
I may be lucky in that I have two blue boards, signifying I have two boards of the same revision.
I haven't tested each solenoid. I was afraid of reversing polarity on the board by trying to test the solenoids.
After looking the board over pretty well, I have determined the power path.

 

Just use a vacuum pump to see if a solenoid will move the door.

 

Ok,
Last night I traced the blue vacuum hose to the vacuum motor right over the hump. I removed the blue vacuum hose, and turned on the engine, and no vacuum to the blue vacuum hose.
In 1986, My car originally (apparently) had a huge phone installed under the right seat, and who ever installed it poked a red power wire through the boot where the hood latch cables go, and when I got the car, I deactivated that thing and disconnected the wires.
I left the power wire in the cable boot for future access if I ever wanted to get a wire inside the car.
I went to auto zone, and they now sell the plastic vacuum tubing in 3 foot lengths on the help section on a purple card. They sell it in 3 different sizes.
I bought the 1/8" size, pulled out the red power wire, and ran that 1/8" tubing in it's place.
I tee'd into the hose that goes to the vacuum ball, and then ran the plastic line to the "blue" motor.

I know, the motor will have vacuum all the time.

ANYWAY,

I doubled the air coming out of the vents.
I think I should Tee into the "pink" motor, and that would shut off the floor vents. and all the air would go to the front vents.
I still have to deal with the broken vacuum line going to the heater valve, but in 105 temps, this is a minor victory. I will wait to fix more of it when the outside temperature goes below 90 for at least a week to insure that the temp won't pop back up to 100 while I have the car apart.
So the problem could be that the vacuum is bleeding off of the heater valve vacuum line and the other stuff won't work if the vacuum is that low.
But now I can feel my face cooling off when I start the car.

 

The solenoids are supposed to actuate depending on the signal from the HVAC control head. I made this chart to show which solenoids turn on when:

There is a custom integrated circuit on the HVAC programmer board that turns on the solenoids. The IC drives a transistor that actually turns on each solenoid. I have been thinking of adding some jumpers so that (for example) transistor A also turns on solenoid B. One of my future projects is to figure out exactly which air doors I want open for the various modes. I'm not happy with the air volume out of the upper ducts when the A/C is on. Also I think I want the recirculation door (orange vacuum line) closed in BI-LEV as well as AUTO.

 

I am beginning to think the controller should have been manual/electronic.
manual to select the doors closed/open
electronic to control the fan speed
semi-automatic to control heater valve
Anyway, it was 99 here yesterday, and I took the car out for an hour's drive.
Huge difference.
I actually was uncomfortable because I was too cold, and had to turn the fan speed down to 8, and I just enjoyed driving around for once in the summer.