defrost not working

[gramps77]

After finding a cracked vacuum line going into the firewall, I was able to get my vents to transition again from vent to heater but defrost is not working. How many lines are there in the system and where else should I be looking.
The vent pointing down for heater selection and then dash vents transition just fine and its very obvious. Defrost simply just never happens.
I realize we are going into summer, but after my dash replacement, Id like to button it all back up with it all working

[gramps77]

Bueller......Bueller...
Anyone?

[Robert1970C20rstbukt]

The defrost mode in my '84 seems like it works when it wants to. I'm thinking the vacuum valve on the control needs to be replaced, I bought one but never got around to installing it. The AC Delco part number is 1571220.

[gramps77]

Where is that part located. I can't find anything that looks like that on my 77. Is right at the back of the sliding switch assembly in the dash?
Posted via Mobile Device

[motornut]

if it's the same as later years
my 88 here has the vac line into the controller above the gas pedal
inside the air box it had three spots for the control rod
it can be set up for always haveing some air up or down
or in the middle is all up or down

[gramps77]

Originally Posted by motornut

if it's the same as later years
my 88 here has the vac line into the controller above the gas pedal
inside the air box it had three spots for the control rod
it can be set up for always haveing some air up or down
or in the middle is all up or down

hhmmm, I do have that thing. I guess I need to replace it. I thought you guys were talking about the box that the vacuum lines all plug into on the lever selector rack that is just about the radio. This would make sense too.

[motornut]

could plug the actual line and run a small hose and try suction ,see if it moves

[gramps77]

So I found that I am getting ZERO vacuum at that valve. I wasnt able to apply vacuum, but I was able to manually close the door, put my finger over the valve, and it stayed until I removed my finger.
So, now to find a vacuum diagram.

[gramps77]

I was able to get it to momentarily work. I am barely getting vacuum out of the ball looking thing mounted to the firewall compared to the vacuum going in.
Also, is it possible for the small white box that is mounted to the lever selector within the dash able to go bad or need lubricated? I dont see how the slide could seal enough without leaking some vacuum