This is an industrial vacuum pump and nowhere does it say to change the oil
after each use. Probably because it was not built for the sole purpose of
air conditioning service. Actually, it used to live at Bendix with about 5
of its brothers running 24/7 to test flight control systems.
Ok, I will check that out.
If at first you don't succeed, you're not cut out for skydiving
I just did a compressor change out on an 1989 F-250. I used a
commercial vacuum pump that pulled a vacuum of around 27. What I want
to comment on is that my FORD service manual states pull a vacuum of at
least 25 for a max of 30 minutes if the whole system had been replaced.
Now 25 is not that great of vacuum and far less than someone on this
group has been saying is required. So far I did everything that the FORD
manual stated and everything seems to be working OK. What I also found
interesting is that the FORD manual said after you disconnect the vacuum
pump make sure that the system will hold that vacuum for at least 5
minutes. Now I do have a problem with this statement. I would probably
be bringing the new compressor back for a refund it is only held a
vacuum for 5 minutes.
It states (the FORD service manual) at least 25 inches of Mercury and as
close to 30 that you came get. You are right that is not the same as 500
microns. So how does microns relate to inches of mercury ?
So what is so magical about 5 minutes why not 2 minutes or 10 minutes or
24 hours ? I help a vacuum over night on the last job with no problem
but the compressor seals would not work in reverse so the vacuum test
was basically worthless as far as telling me the seals were good ?
Nathan W. Collier wrote:
Micron is really almost a useless measurement to almost anyone that is
reading this newsgroup. It cannot be measured with the equipment
available to the service or home repair person. Vacuum pumps are
specified in volume/sec and inches of mercury. Volume is not important
to us because we are working in a closed system if we had a hole in one
end and were trying to keep a vacuum inside then volume per minutes
would be very important now I sure hope everyone knows that you must
have your AC system closed before you start drawing your vacuum. So now
all we need to do is determine what the min vacuum we need to pull and
from what I understand now about this subject almost anything that will
draw a vacuum will work just fine on our AC systems if it can acheive a
certain ?? inches of Mercury. So now lets get off this micron issue and
on to something that we all can measure. If a manufacture of a specific
vacuum pump states it can draw 50 micron then at what inches of mercury
are they talking because then any vacuum pump that can achieve that pull
will do that same thing, volume again is not important.
Ron in Phx, AZ where AC is required.
.....if you dont care about doing the job properly that is.
?? i paid less for my micron gauge than i paid for my pressure gauges.
if it can pull 500 microns it will work just fine in your a/c systems. if
it wont (and it wont) its _not_ "ok" to use it. sure it will make the
system run and cool but it will NOT cool as efficiently as it would if it
were done right. the suggestion that it will is irresponsible at best.
No, any self respecting residential service tech has a micron gauge.
I don't have a clue how often they're used in automotive AC but I
suspect not often.
A micron is 0.001mm. There are about 25400 microns to an inch. A
gauge set simply doesn't have the resolution to measure a 500 micron
BTW, a perfect vacuum would be 0 microns. 500 microns is 0.5mm.
Micrometers... 1 millionth of an inch. 1" of Hg = 25,400 microns of Hg.
However, the scale is inverted. In other words, a perfect vacuum (29.921"
of Hg at sea level) is 0 microns. Therefore, 500 microns is about 29.903"
OK got that one answered now I would like to see a temperature chart of
the center register discharge temperature versus vacuum drawn on your
typical fixed orifice tube auto AC system.
From No vacuum pulled in five degree steps to 29.903 which is almost a
I personally believe that what you will see is a straight line or two
straight lines with anything between these two temps being OK and that
vacuum is not related to the temperature output on your typical auto AC
at all. The size and condition of the system, the fixed orifice tube
and the amount of oil in the system will set the output temp.
Please prove me wrong on this because if a super vacuum will get my AC
20 degrees cooler here in Phx, AZ I am for it.
I did see yesterday that there is a new fixed orifice tube that is
really not fixed but variable that is claiming 12 degree better cooling
at idle of course I found this after I filled the system with a new
charge. If I had a recovery tank I would be installing one of these.
The purpose of drawing a vacuum is to get the moisture out of a system
that will cause corrosion and I real believe that is all. Right or
Wrong ? I need hard facts or a website that explains this in detail if
a vacuum will really drastically improve cooling.
if you have moisure or non-condensables in your system it cannot possibly
work as efficiently as it would if it were pulled down into a proper vacuum.
nobody said 20 degrees. if you pull a vacuum with a pressure gauge and a
refrigerator compressor you might see a difference of 8-10 degrees. if you
use a better vacuum source the difference may only be 1-2 degrees...but
there will be a difference. we within the industry dont spend $300 for a
decent 2 stage vacuum pump for the hell of it. we do it because as
professionals we want to give you the best service possible and that means
doing it right. if the cheaper alternatives were "ok" we would certainly
use them (i got dozens of compressors of all types and size that it ok off
jobsites in equipment being replaced) and same some money.
and non-condensables which hinder cooling and can be fatal to compressors
and metering devices.
Now that sounds a lot better 1 to 2 degrees is not worth my money as a
home repair do it yourself person unless I can find a good suction
pump used really cheap. When it 120 ambient and the inside of the car
is in the 160 degree range 1 to 2 degrees will not be detected. 10 to
12 maybe but questionable. I have no problem with a professional using
the best possible tools if they understand them and aren't just using
them for show. I am afraid most do not understand them though and might
not even use them most of the time.
I turned my AC on this morning. I installed a new compressor yesterday.
The air was so much colder I turned the fan down to low and all of a
sudden got smoke that smelled like wood burning coming out of the vents.
I thought about it for a while then determined there must be something
in the resistors that control the fan that got burned. Sure enough it
was packed with leaves. I did get a good look at the evaporator and
could see that it was really packed with stuff also so off with the
sides to see if I could wash it out. Got the garden hose with a high
pressure nosel on it and now it looks like it will pass some air. I
have no doubt that it was almost 50 per cent restricted. Just about
ready to reassemble and see now much better it will be.
So how do all these other non-condensables get into a closed system ?
Moisture I understand and metal parts for things breaking but if the
system came from the factory with a good charge and then a seal started
to leak I would not expect to have anymore non-condensables in the
system after I replace the compressor than before I replaced it other
than mybe some moisture from having the system opened.
Back to work (I guess a retired person shouldn't use the word work so
back to my fun project)
Nathan W. Collier wrote:
bear in mind that its also an issue of compressor/metering device damage.
it may only shorten component life by a little, but it will shorten
its no longer a closed system once you open it to replace the compressor or
other components. you also have component disentigration, minute particles
left from machining the new components, etc. where you have moving parts,
you have wear.
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