in response to a message on the Corvette Forum # 312436
.74 didn't come with a vacuum shut-off for water flow to the heater core?

There are solutions to a C3 vette that has no hot water valve to prevent hot water from flowing through the heater core.

1. Cap off the hoses that feed the heater core. This is NOT recommended since it prevents the heater and defroster from operating properly unless the hoses are reconnected.

2. Add one or two manual shut off valves in line with the hoses feeding the heater core. This is also NOT recommended since it prevents the heater and defroster from operating properly until you pop the hood and open the valves.

3. Add an original type vacuum operated hot water shut off valve and connect it to the vacuum source that is mounted to the heater/AC controls under the shifter console. Although this solution requires a couple of additional hours of effort, it allows all climate control functions to be operated right from the drivers seat. These vacuum operated valves can be added to any air conditioned Corvette that did not have them, and any non-air conditioned Corvette - except 1968.

Check out the color Climate Control illustrations.