jonesolds442

Hello all,

('70 A-body with a/c)

Hot air is not being dispersed even though the heater control valve is functioning properly and the heater core is not leaking and has unobstructed flow. My only guess now is that inadequate vaccum is not allowing the control head temp selector diaphram to be fully opening; I was performing a hail-mary jigglefest with all the control head settings (vent type and temp) and temporarily got hot air before it went back to lukewarm.

Your thoughts?...

Lady72nRob71

Sounds like a vacuum leak in the control head if "jiggling the handle" got it to work a little.
Check the vacuum line going from the control head to the valve for cracks, splits, etc.
Try using a small vacuum pump on the hose inside and see what that does. I am cheap, so i will attach a clean section of hose with a coupler and suck on it with my mouth... If that get the valve open and heat going then it is the control valve int he panel.
Some of these water valves require vacuum to open, while later ones require vacuum to close (as a failsafe). If your valve was changed, verify you got the right one.