How much vacuum at heater control valve
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,395
Likes: 1,225
From: Tampa Florida
How much vacuum at heater control valve
Does anyone know how much vacuum I should have at my heater control valve with controls in the off postition. I'm only getting around 5" of vacuum, and I don't think that amount will keep it in the closed position.
Thanks
Thanks
Safety Car
Joined: Oct 2007
Posts: 3,729
Likes: 267
From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
depends on your base vacuum. unplug all your vacuum hoses and put a vacuum gauge on ... it should read 10-20 the higher the better,
(Big Cam= low vacuum) your Heater vacuum line should be close to your base vacuum.
If not you got vacuum leaks somewhere..
good luck,.
(Big Cam= low vacuum) your Heater vacuum line should be close to your base vacuum.
If not you got vacuum leaks somewhere..
good luck,.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Vacuum should be the same as manifold vacuum. Vacuum holds this valve closed with the controls off (or A/C on). When the engine is turned off, the vacuum goes to zero and the valve will open letting hot engine coolant percolate through the heater core - not too cool when you return to your car in the summer! Many will add a second mechanically operated valve in the line to (or from) the heater to stop the coolant from adding to the heat in the cockpit.
Last edited by larrywalk; Aug 7, 2008 at 10:32 AM.
Le Mans Master
Joined: Aug 2006
Posts: 7,413
Likes: 1,552
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
On my 74 w/AC there is no vacuum to the heater control valve in the off position. When I turn the thumbwheel to Hot I get 8" of vacuum and the valve opens to allow the water to go thru the heater core. PG.
