Posted by George Goble on October 22, 2000 at 21:07:54: via: or 128.211.159.11
In Reply to: Moisture in posted by Bob P. on October 22, 2000 at 13:40:15:
oil bubbling in charging cyl under vac...
This is normal.. probably mostly trapped air coming out.
With Mineral oil, Vac could "boil" out the moisture..
Method: need a good micron vac gauge (Dont use a supco,
you can suck on a straw and make it read 50 microns), and
blank off (valve off) vac pump, while reading microns on
the system (or oil) under test.. If you can hold under 1500
microns (at about 70F).. then system is dry. Any moisture,
will cause reading to rise to 1500ish and stay there when the
pump is blanked off. If leaking, reading will keep rising
past (above) 1500.. when reading rises to 25,400 microns, you are
at 29.0 "inches" of vac on the manifold gauge. 0 microns
is the perfect vac (30.0 Inches) and is not obtainable.
Good two stage vac pumps with clean oil can do 25-50 microns
when just connected to the gauge. The presense of "mineral
oil" in the system will limit the best "blank off" vacuums to
150-300 microns, as that is where mineral compressor oil boils.
With mineral oil.. any vac that holds (blanked off) for 5 mins
at less than 1500 microns means a dry system is good in practice.
Many PAG oils are much more volatile than mineral oil (and water)
and may not even allow a blank off vac of 1500 microns to be
reached as the oil may boil before the water does... A vac
will not dry out a system if this is the case.
It is possible (takes a long time) to dry out dryers (mineral oil)
with a vacuum.. lower than 1500 microns.. heat not needed.
Heat also works (need to be < 300F or so as not to melt
plastic support parts in dryer, but you also need flow of
dry nitrogen if drying out in an oven).
When installing a new dryer, make sure you get a hiss or suck
when pulling the cap off.. this means it was packed well.
no his or suck.. means dryer could be "beathing" (not sealed)
when in storage, and as atm press changes, moisture gets sucked
in and after a few months it is water logged.. Not too much of
a problem with R12/mineral oil or HVAC/R22/min oil.. since the
usual 30-60 min vac took out 5-10% of the moisture [from the dryer]
and that is enough to keep sys dry and will keep a dry-eye green.
If you have PAG OIL, IT MAY boil first, and no moisture may
be removed.. and hence all the problems.
Sporlan Dry-eyes ("see all?") go green at below anywhere between
5ppm and 80ppm moisture, depending on the temperature and
the refrigerant in use. Colder temps make them more sensitive
(turn green at less ppm).. See www.sporlan.com .. they have
charts.
Green UV dyes (for leak detection) and the older Red "Dye-tel"
dyes in oils ruin the salts in the dry eyes... Green dye perm
stains the eyes green.. so techs think their recovery machines
have dry refrigerant, when it is really wet (yellow).
It is possible to hook a Sporlan dry-eye to a 134a quick
connect (car not running), via a "goose-neck" inverted
U tubing, and immerse the dry-eye in a glass of ice water
to condense some vapor 134a into liquid in the eye to
leave the dye behind and get a good moisture reading and
not trash the salts out. Remember to pull a deep vac
on the eye first and pre-charge with a little dry 134a vapor
first. When done.. holding the eye in your hand or warm water
boils the liquid back out and returns it to the system before
disconnecting it.
--ghg