On my 1969 firebird with 350/350 automatic, 2 barrel carb, the Thermal Vacuum Switch has a port label "CA" on the body of the switch and is supposed to be connected to the curly line that attaches to the front of the 2 barrel carb.
What does this do.
The "DA" port is of course connected to the distributor.
The following diagrams from the '68 Diagnostic Manual should help you. They show all the routing, functional diagrams, etc. for that vacuum system. Although the diagrams for '68 show the use of all five of the TVS ports but a Pontiac Service Bulletin (T-2 if I recall) later eliminates the vacuum retard function and loops/closes off two of the ports. If you would like to see the '68 Service Bulletin, I believe I have one somewhere. Just let me know and I'll look for it and send it to you.
Thanks, After following the diagrams I still do not understand what the CA(carbur Advance) port actually does. 1. Why does there need to be vacuum applied to the Carb.
2. In looking at the digrams and various threads on the TVS it seems as if there is no distributor advance except when the engine reaches a certain overheated condition. Most engines I have worked on there was vacuum source for the distributor advance that kicked in during acceleration?
According to Pontiac Enthusiast, Vol 1 No. 2, 1968-69 Emissions Systems Tech Part 2 TVS, by Peter Serio (possibly he will also respond here) the TVS has two purposes. First, it is a safety device to help prevent overheating. "Whenever the coolant temperature rises above 230 degrees F, the TVS switches the distributor advance from ported to full manifold vacuum. This advances the timing about 20 degrees at idle, allowing the engine to cool down to normal operating temperature." Second, in some '68 models there was a vacuum retard to reduce emissions
