A/C vacuum only goes to -20psi, but holds?

[Jacob Burnetski]

My A/C system in a 94 Crown Vic was completely empty of refrigerant.
I replaced the accumulator, o-tube, and a bunch of o-rings. When I
put the vacuum pump on it and let it run for 50 mins or so I can only
get the vacuum down to -20psi. I shut it off and it holds there
(going on 3 hours now with no change)

If there was a leak in the system wouldn't the vacuum give up over
time and eventually equalize? Is this just as low as I'm going to get
it?

[Stan Kasperski]

I'm not aware of any place on earth's surface where you can get -20 psi
relative to atmosphere pressure by vacuuming. Atmospheric pressure at sea
level is less than 15 psi. Sounds like you need to get gauges that work
properly. If you cannot get somewhere near 30" Hg (inches of mercury)
vacuum, then there is something wrong with either your gauges or your
vacuum source. Test the gauges/vacuum source by hooking the gauge up
directly to the vacuum source. Should be able to pull near 30" Hg almost
immediately.
Stan K.

[Garrett Fulton]

"Jacob Burnetski" <JFB...@hotmail.com> wrote in message
news:u9v5kvghtrv44ai1j...@4ax.com...

You've got a small leak somewhere between the pump and the line fittings on
the car. Air is coming in and causing the lack of full vacuum. When you
close off the car's system, it holds at whatever it has been pumped down to.
Which is good. You'll need to find the leak. Had it happen to me and it
was a bad o-ring on the adapter that goes from the gauge lines to the car's
fitting.

Garrett Fulton

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[Elbert Clarke]

thats normal.... if you can pull down to 20psi and it will hold that,
then you are good.

----
Elbert Clarke
eecl...@earthlink.net
elbert...@us.army.mil

[bobby]

Some vacuum pumps also have a ballast valve that intentionally lets air in to
dilute condensables (you don't want to try to compress something into a liquid
as the liquid is incompressible and will be more likely to mix with the oil and
lower it's vapor pressure). As Stan and Garrett have mentioned, first verify
you don't have a leak in the hoses/gauges. I'd start by connecting the gauge
directly to the pump. If it hits 30in Hg, pump is ok. If not, look for a knob
on the pump somewhere and turn it to close the ballast if it is so equipped.

Good luck,
bobby