[Red Box Rebel]

Anyone know where to get a diagram of the vacuum hose routing for the A/C Heater control switch under the dash?
There is a vacuum line coming in from the engine compartment through the firewall and connects to the ported vacuum switch that is part of the a/c and heater controls.
One of the vacuum lines coming out of the ported vacuum switch goes back through the firewall to the valve that controls hot fluid going into the heater core.
My problem is that I do not know where each line is supposed to be placed on the ported vacuum switch and what device each line is connected to. A diagram and/or a description of each line would be helpful.

[dataway]

This might help, it's for a 68 ... sounds like the valve you are talking about under the hood is the heater control valve ... which I was pretty sure didn't show up till 1969 ... any chance your AC was retrofitted from a later model?

I don't think 68 has that extra vacuum line going back under the hood, just one coming in and supply vacuum to the controls.

[OG68]

Agreed.

68 A body did not have a water valve but 69 did. And the water valve is controlled by a separate or second vacuum valve mounted on the controller.

[Red Box Rebel]

Originally Posted by OG68

Agreed.

68 A body did not have a water valve but 69 did. And the water valve is controlled by a separate or second vacuum valve mounted on the controller.

Thank you for your reply, but my '68 GTO with factory A/C has a water valve.
It is vacuum operated and my problem is which vacuum line operates the valve.
My vacuum lines were destroyed in a fire and all had to be replaced. That is why I need a diagram to know how to re-plumb all the vacuum lines.

[Red Box Rebel]

Originally Posted by dataway

This might help, it's for a 68 ... sounds like the valve you are talking about under the hood is the heater control valve ... which I was pretty sure didn't show up till 1969 ... any chance your AC was retrofitted from a later model?

I don't think 68 has that extra vacuum line going back under the hood, just one coming in and supply vacuum to the controls.

Thank you! I will study the diagram and determine if it will work with the A/C

[dataway]

Bear in mind that the diagram is for a 68 Tempest/GTO, so it's not going to show anything for the heater control valve.

Here is a diagram for the 68 PONTIAC vacuum lines. It DOES show the controls and lines for the heater control valve.

I guess pick the one that looks the closest. In 68 ... at least according the factory literature the 68 Tempest/GTO did not have the heater control valve (started in 69). The big Pontiacs did have the valve. This diagram shows the layout for the big Pontiac AC system with the heater control valve.

Bear in mind ... if for some reason your 68 has a 69 AC system installed, there are minor differences ( Like the heater control valve) and you might need to track down a 69 diagram. These diagrams are from the 68 Pontiac Pontiac Diagnostic Manual.

[OG68]

The diagram below is for a 69 Tempest/GTO. It has the second vacuum control for the water valve. Maybe you can use this.