1955 heater vacuum valve open or closed

zeroroadkill

Active Member
On my ‘55 there is a heater water valve which is controlled by a vacuum valve under the dash on the heater plenum. The vacuum line runs to the windshield wiper motor and tee’s off to the heater vacuum valve which is controlled by the dash heater temperature lever cable. When there is no vacuum to the heater water valve the valve is open letting hot water flow to the heater core. When vacuum is applied the heater water valve closes reducing the flow of hot water to the heater core. Moving the temperature lever to high moves the vacuum valve up which in my case let’s a small vacuum go to the water valve shutting the water valve down and when the temperature lever is put to low this moves the vacuum valve down shutting off the vacuum to the water valve. Backwards!!!
If I slide the temperature lever to high it gets cooler and if I move it to low it gets hotter!!!
What’s going on here??? Is the vacuum valve mounted upside down?

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zeroroadkill

Active Member
Good point! No markings on it. I noticed it was mounted by the heater blower motor and not on the intake manifold too...
Found it online - generic. Probably works backwards from OEM!

Just ordered one that opens with a vacuum.
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