On Wednesday, December 31, 2014 7:13:44 AM UTC-5, mike wrote:
On 12/31/2014 12:40 AM, Danny D. wrote:
mike wrote, on Tue, 30 Dec 2014 23:48:14 -0800:

I have never seen an actual system, but I surmise that there
may be a vacuum relief valve somewhere so the motor gets
cooling air if you leave it on with all the ports closed.
That might confuse your diagnosis.

That makes sense, but, (a) I have never seen a vacuum relief
valve (but I don't know what it would look like), and, (b)
there is no suction unless/until I open a spring-loaded hinged
port, and press in the hose.

When I press in the hose, an electrical contact is made,
which turns on the vacuum in the basement.

I don't know *any* other way to turn on vacuum, other than
to press in a hose. So, when all ports are closed, the
vacuum doesn't work. When any one port is opened, the vacuum
doesn't work.

It's only when electrical contact is made that the vacuum
turns on (but it's far too low to be useful).

It's night now, but I'll snap a picture of the vacuum
itself, in the basement, in the morning, and post.

You probably have a rubber hose on your auto vacuum gauge.
Poke it down the suction hose and seal it with a rag or
duct tape. Doesn't have to be a perfect seal.

It doesn't have to be perfect, but it has to be consistent and
not change. Otherwise the reading from one outlet to another,
where he's looking for a difference in pressure to track down
where the leak is closest too, would be meaningless. Personally,
I don't think a rag or some tape is going to be easy to do.
He has to take an auto size hose, which is ~1/4" and get it connected
to something that is ~1 1/14".



Stuff the other end of the suction hose into one of the ports
to turn on the system.
What you want to know is whether the vacuum goes up when
the volume goes down near zero. Based on your statement that
there's air coming out the exit side of the central system,
You probably don't have a blockage.
While you're in that mode, go around listening for air leaks.

Another thing you can try is to duct tape the suction
hose to a canister vac hose and plug that into the port.
Pull the fuse so the central vac doesn't start.
Turn on the canister and go to the central unit and listen
for air leaks.

Is the piping separate branches or taps of one branch?
You may be able to put the canister on one port and
stuff a rag up from the central sucker and learn which
branch has the leak and doesn't suck. If it's tapped, you may be able to
tie a rag on a string and learn which two ports straddle
the leak. Just let the vacuum suck the rag into the port.
If the leak is beyond the port, you'll be able to tell
that the rag gets sucked hard as it hits the tee.
Tie the rag securely, or you'll have a blockage
to go with your leak. Get help. You may need to pull the
motor fuse to get the rag back out without damaging something.
Paper towel on a string would be less risky. There's probably
screws sticking thru the pipe just where you don't want them.

If I had to bet money, I'd bet that the central system
is built from sections held together by something that's
no longer holding and they slipped apart. Snaking it probably
didn't help that problem.
I recently crawled around in the mud to fix my neighbor's
dryer vent that had just slipped apart when the tape failed.

The above is "stream of consciousness". Might be better to
do the easiest stuff first from the bottom up.