No vacuum to HVAC system, stays on defrost

[Buford T. JuSStice]

Okay, so I've got my wagon all tuned up and running as well as I think I can get it. I gave up trying to use an engine analyzer to tune it, and used a vacuum gauge instead.

Adjusted static timing, then the idle mixture until I got about 14-15 inHg at 950rpm idle. It has a 383 Blueprint stroker so I guess that's the best I can get out of it with the cam it has. It's relatively smooth though so it's good.

Got the blower motor to work, but I have one problem... I can't seem to get the vacuum actuated doors to work and switch from defrost to vent or anything else. I get plenty of heat out of the defroster, but if I want to push air out of the vents, it just won't do it.

I've got to test the box to see if I need to change the actuators, but in the meantime, I think it might just be how I'm getting vacuum. I'm not sure where to draw from on this. I'll provide link to my carburetor, hopefully somebody can provide some insight on how to set up the vacuum to the heater box.

Right now I've got the little ball on the passenger side fender with two vacuum ports going to it. One port has a grey tube, the other is purple. I've got the grey one going to the front right side port on the carburetor (normally used for EGR) and the purple one going back to HVAC. From the HVAC there's another tube that I have going to the heater hose actuator.

https://www.summitracing.com/parts/sum-250216

 

[MrSony]

The ball has the purple on the small nipple and vacuum source from engine on the larger nipple. Put a 1 way check valve on the source like. Grey line should go to the heater valve.

 

[69hurstolds]

Maybe these diagrams could help? If all the lines are ok and vacuum signal is good...it may be the selector valve in the head unit disc may not be in good shape or one (or more) of the mode valve actuators' aren't cooperating.

 

[Ribbedroof]

You want manifold (constant) vacuum to the ball. Originally, it would have come from a fitting in the intake behind the carb, usually also is the source for trans modulator on those so-equipped.

The system defaults to defrost in case of vacuum loss as a safety measure

 

[airboatgreg]

After manifold vacuum thru ball pull out interior controls and make sure you have enough vacuum. Most likely the rotary vacuum switch is bad if getting vacuum to the switch does not fix it.

 

[Buford T. JuSStice]

Okay, so I've got some diagnosis and checking to do. I've already tapped into manifold vacuum with no progress, so something under the dash could be the problem.

 

[MrSony]

I had to drive my car a little to get enough vacuum to get it to switch.

 

[airboatgreg]

So after driving did it switch to the vents?

 

[Buford T. JuSStice]

Negative. I tested all the doors with a vacuum pump and they all seem to work just fine, I tried pulling vacuum from the violet tube out in the engine bay, but couldn't get any vacuum at all regardless of what setting I had it on inside. So I'm guessing the plastic tube may have a crack in it somewhere, or it's not fully seated in it's little firewall grommet. Either way, at least it's progress to zeroing in on the spot.

 

[Buford T. JuSStice]

Either that or it's the rotary... now that I think about it, looking back at the trouble shooting tree, I didn't actually test that. I went straight to the doors to make sure they were fine.

Looks like I'm gonna have to test that out, and if the doors work going from the connector, it's the rotary. I wonder if that's something I can take apart and tinker with hmmm...