AC /Heater control Vacuum system

[wicky88s1975]

Alright, I have a 75 coupe I purchased in AZ, After bringing her home a few months ago I found out that CA has very strict Emmission Laws. Most of the problems I've had in the past months came easily solved through Reading publications Internet searches and other owners I know. The newest problem is the vacuumtube system for the AC Heater control. Does any one have a diagram of it. I need to figure out which tube is suppose to operate the heaterhose shut off valve. I dont have a tube that isn't doing anything and the GM assembly book wasn't any help. in advance THANKS Jim (new at restorations)

 

[Big Fish]

As near as I can tell there should not be a vacuum controlled valve in the heater hose. Are you pretty sure it is original equipment? All my schematics show only vacuum operated doors for defrost and temperature contol. :confused

 

[wicky88s1975]

I don't have the schematics so I'm just Guessing. The assembly manual only has drawings that aren't very clear as to what perates in any given postition of the dial. Do you have the schematics and can you e-mail them to me? The heater shut off valve was listed as 75-77 part at Zip so I "assumed" it was removed by the previuos owner.

 

[Bob Chadwick]

On the 77, there is a white vacuum line, so small it looks like a wire and likely yellow by now, that comes out of the firewall near the distributor and snakes across the front of the firewall and down the passener side of the engine compartment where it passes near the radiator overflow and down to the water line going to the heater core.

On my 77, vacuum is sent to the valve by a vacuum switch on the top of the heater ductwork. When you slide the slider that controls the temperature mix to the cold side the mechanical cable that controls the ductwork pushes an actuator against this vacuum switch and sends vacuum to the valve shutting off the supply of hot water to the care.

I took this out of my heater line and added a manual shutoff that works much better.

There are numerous posts on this issue here, alot of them mine because of the problems I was having, so if you do a search you should find alot of information.

Bob

 

[wicky88s1975]

Thanks Guys for your help. I looked alot harder in the assembly Manual and I did find the schematic of the hoses coming out of the ac/heater control. and my problem was solved. I installed the shut off valve in line and then put a "T" fitting in the AC line. This suts off the heater during AC operation and when the system is off. Thanks again.