If it were me, I would render the thermactor inactive in the wide open
position and eliminate the vacuum line and potential leak. We use these
coaches pretty much in the summer season, so that air cleaner flap is of
little value. Jwiwd.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Oct 8, 2017 2:01 PM, "Jack Christensen" wrote:

I'm tracking down vacuum leaks on my 455.

The flap that allows warm air from the manifold to get to the carb and help
during startup is controlled by a sensor mounted in the air cleaner assy.


I found that the sensor seems to work properly in that when the engine is
cold, vacuum passes to the flap controller and operates it causing warm air
to enter the engine. What I also found was that when the sensor warms up
it does cause the flap to release as it should, but the sensor then leaks
vacuum when it's warm. It's not a whole lot, but more than I would have
expected. I would expect it seal off the vacuum. Is this usual or is the
sensor bad?
--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

Thanks all,
I like Jim's suggestion. I've never had anyone during the smog check do more than look to see if the hose to the manifold was present. No test of the device. I'm devious enough to make it look like everything is OK.

Wrong. No vacuum signal is open by return spring (cold air)
Vacuum moves the door against spring tension to closed (hot air from manifold stove)