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Lloyd E. Sponenburgh[_3_]

fired this volley in news:2c4abdd1-d0f0-40dd-a32d-
:

I purchased a used Robinair 15102-A vac pump last winter (much better
price off season). Now I am ready to use it. I added oil (did not
replace the old oil since I was doing a test evacuation) and hooked
the vac pump up to the vehicle's A/C system. I was able to pull 26 or
27 in of Hg of vacum. As I understand it I will need to pull 29 in of
Hg to properly evacuate the A/C system (after repair).

Will changing the oil have an effect on the pump's performance (pull a
stronger vacuum)? I searched for a manual or an exploded view of the
pump with no success. What other sort of maintanence might I need to
do to the pump? Other than hooking the pump up and letting it run,
are there any other proceedures that I should / need to follow?
Suggestions / links to info very much appreciated.

You _cannot_ determine the degree of vacuum necessary to properly dry and
fully evacuate a system with only mechanical gauges. You need a
thermistor-style vacuum gauge. They aren't expensive.

I'll give you a scenario as to why. Yesterday (yes, actually) one of my
employees asked if I could check out her Toyota's AC (which was blowing
hot). yep. I grabbed the manifold gauges, the 134A adapter fittings,
and the vacuum pump (Robinaire 6cfm). New oil, by the way. Always new
oil -- AFTER every pull-down. Always. Never not. No excuses. ALWAYS...
(did I say, "always, every time, no excuses, ALWAYS? If not -- ALWAYS,
after EVERY pull-down on ANY system of ANY size. Oil is cheap, pumps
aren't and inadequate pull-downs even less-so).

ANyway...

She complained that several people had "charged" her system using one-
hose taps, and it was blowing hot. So I told her to go get two cans of
134A, and let me just pull it down. If it had a leak, we'd know. She
could get the leak fixed professionally (I don't DO auto repairs except
on my own vehicles).

I pumped the goop out of her system (full of leak-check and excess oil),
then hooked up the pump and thermistor gauge, and let 'er run. I was
hoping for 200 microns (mercury column) of vacuum. After three hours, it
wouldn't drop below 400. That's sort-of a sign of a leak, but I had a
clue that said, "no".

By the way, do you know what 400-micron vacuum looks like on a mechanical
gauge? (clue -- about the same as 1000-micron vacuum)

ANyway... the average vacuum wouldn't drop below 400, but the thermistor
gauge would occasionally dip to 275, then suddenly JUMP back to 400.
That's not the way they normally work -- they move _gradually_ from
point-to-point. They never jump -- unless. Unless there were droplets
of water entrained in oil in the system, and they were progressively
exploding into vapor, literally one-at-a-time.

Another clue was that the oil in the pump sight glass was growing cloudy.
It never does that on a healthy system. Only on one with lots of water
in it.

BTW... do you know what water looks like in a mechanical gauge? (clue --
about the same as no water, only there's an important distinction
concerning how the system will work with or without it, and the gauges
don't tell you that)

So... we let it run; All of 6 hours plus, actually. It pulled
"droplets" for almost the whole time, gauge slowly moving down to 275,
then jumping up to 400 again suddenly. Then, in the last 30 minutes, the
thermistor gauge started indicating improvements. Eventually, it held 50
microns on pull, and rose to only 200 after being off the pump for 10
minutes. That's a good pull. No air, no water, nothing to interfere.

A quick re-charge was all that was left -- and you already know how to do
that.

Quick answer -- no... you can't tell with mechanical gauges.

LLoyd