Vacuum line for heater control valve

[Booie]

I just changed my heater hoses and a new heater control valve but the vacuum line was off the other end it was just laying behind the motor by the distributor. Does it run through the firewall to the controls it is not very long so there must be some connection I am missing.
Thanks

 

[6880 Mike]

Yes. On AC cars, the vac line runs from the console control, through the firewall, and down to the shut off valve. A second line runs over to the flapper door on the cowl.

 

[Booie]

Thanks 6880Mike Do you know where it comes through the firewall at.

 

[Bob Chadwick]

Right behind the distributor. I've never been able to figure out whether it goes directly down to the heater controls or attaches to a fitting at the firewall.

 

[bmotojoe]

Actually there are three vacuum lines through the rubber plug in the firewall. The black line is the vacuum source, the green line is the plenum door control, and the white line is for the hot water shutoff valve in the heater hose line. The black source line tees just on the other side of the firewall (inside of car) feeds both the main heater control and the water shutoff switch (Located on top of the heater box). When you slide the heater control to cold the cable is connected on top of the heater box and presses an arm against the vacuum operated hot water shutoff valve switch, once the vacuum switch is made is sends vacuum to the hot water shutoff valve in the heater hose line closing the valve. The vacuum operated shutoff switch does dry out over time and will not function correctly. Best to test with a vacuum gauge on the hose at the heater hose shutoff valve, there should be 8 or more inches of vacuum there if not then the vacuum switch is bad or a bad line. There are replacements from most vendors but the spring in them is too heavy for this application. I have a good repair tip for retrofitting the new vacuum valve switch to work correctly.
Brian

 

[jjarrett]

to bmotojoe--reading your post you mention a h/c water switch on top of the heater box.can you post a picture of this? i have a 76 coupe and the heater assembly is removed,but there is no switch on the top.what would i order if i need this part?--thanks---john

 

[bmotojoe]

I’m sorry; this vacuum switch is for 1977-1982 cars. I have been looking through the parts book for the 1976 to see how the earlier models do the switching but have found nothing yet. Do you have a copy of the assembly manual for your 1976? Maybe someone here can display the heater control section here for you. Sorry I can’t be of more help.
Brian

 

[jjarrett]

thanks for the reply Brian! yes i do have the assembly manual,but it does not show the top of the heater very well.when i bought this 76 there was no heater or a/c ,so i bought a heater box and the ducts.that is why i don't know if i'm missing parts or not. and i can't find the white vacuam line that goes through the firewall.there are three lines in the grommet but i don't see a white one.one of them goes to the right up under the fender,but has rotted away.i guess i will get it sorted out after while though.thanks---john

 

[bmotojoe]

John, I found a parts drawing in the Corvette Parts book showing the heater control system. There is no vacuum switch on top of your heaterbox like 77-82 have. But I think I found the vacuum switch that controls the hot water shutoff valve in the heater hose for your applacation,,,I think.
I can send you this drawing if you like. PM me with you e-address and I will get it off to you. The drawing is to large to post, and if I shrink it up to post you cant read it very good.
Brian

 

[Booie]

Thanks Everybody you all were a great help. just bought my car July 3 and have got a lot to learn.