BILL88

hi, i have 1966 corvette a/c coupe, had my car on the lift today, noticed a vacuum ling hanging next to the stv valve .traced it up to a t connection, one end was hooked to the intake manifold other going through fire wall. should the line hanging down go to the fitting on the bottom of the stv valve?
thanks much, bill

Nowhere Man

one vacuum line should go into the hot water shut off valve on the heater hose next to the firewall

mark6669

yes there should be a plastic fitting that is screwed on to the bottom of the valve with a vac hose.
Mark

Mike Geary

The T on the firewall takes vacuum from the intake manifold fitting and sends it in 2 directions: a: straight down to the bottom of the STV, and b: thru the firewall into the vacuum switch on top of the inside air diverter box.

Coming out of that brass vacuum switch, the rubber line feeds back thru the firewall grommet to the coolant flow valve on the inlet to the heater core.

Vitaminmopar

The diagram in post #4 Mike G supplied shows a vac line connecting to the STV. And Mike pointed out the routing. A point of clarification as the STV does not have a vacuum line nipple to attach too. I think 66 has two STV configurations. On your 66 if you see a small black housing next to the STV that is the APV (Absolute Pressure Valve) and there should be a vacuum line connected to it. If you have a metal diaphragm can on the end of the STV, the vacuum line would connect to it. You should also have a hot water cutoff valve which requires a vac line also as Mike stated.

Mike Geary

Personally I consider the APV to be a part of the STV assy since it's actually attached rather than "next to", but it's not worth debating.