Hook the hand pump directly to the damper motor. When you pump it, you should see it's rod move. Once it moves as far as it can, you should be able to give it a couple more pumps and it should hold with no leak down.

 

Hopefully, it's as simple as the check valve, but if not, I have plenty of stuff to check, and now I know how to do it. Another thanks to everyone who has weighed in on this topic to help out with great suggestions on what could be at the root of the problem. There is no way I would have been able to find enough time to discover all the possibilities by myself. Forums like this are worth their weight in gold!

 

you might try a cheap trick: a Cigar and smoke

watch this video: test vacuum leak with cigar - Bing video

 

.....and I just happen to have a big ole stogie waiting in the garage for a celebration. Looks like it will soon be up in smoke!

 

well ? did you light it up?

 

No time yet. Hope to get on it again one day this coming week. Plate's been too full lately....

 

We've seen it all.

I've had two bad HVAC vacuum check valves over the years on my Aeros.

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