"Bill Noble" wrote in message
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"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.70...

interesting stuff snipped ----------

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

LLoyd

interesting post - I wonder if where you live matters

I have repaired a number of cars where the AC system is empty - mostly
944s in fact - swap the seal on the pump put in some of the new oil for
R134, and fill - works fine. on one that exploded a hose in 130 deg
weather, just replaced the hose (a few weeks later), and it worked fine.
Never saw any moisture effects. So, why does your experience differ?
could it be a drier climate, or could it be something else? Note, I am
not questioning your advice/report, it makes perfect sense, I'm wondering
why I can get away with not doing all that stuff?

Possibly the systems you worked on were clear of moisture before you opened
them, and you had them open for just a short time, so the amount of moisture
in the system was minimal.

I do commercial HVAC service and all manufacturers recommend pulling a
vacuum of 400 microns or lower to remove moisture from the system. If the
system is new, and relatively clean you can reach 400 microns in minutes. On
the other hand if the system has moisture in it it can take hours, or even
days to pull a system down to 400 microns.

One time I vac'd a system for about 60 hours before it would hold less than
400 microns. The year before another service company replaced the compressor
that failed. I replaced the compressor a second time, ran the vacuum pump
for about 24 hours, changed the oil on my vacuum pump, purged the system
with nitrogen and pumped it for about 24 more hours, changed oil on my
vacuum pump again, purged the system with nitrogen again, them pumped for
about 12 more hours. At this time the vacuum held at about 300 microns. That
second compressor has been running for over 6 years.
Greg