The AC school I recently attended taught to go by Hg when evacuating a system. I can see from this website and others that a micron gauge should be used. My question is, do you just pump it down until the desired level has been reached or is there a procedure that should be followed. Also, what is the target micron level? Finally, can someone recommend a good micron gauge?
Vacumn By HG
What a joke. I wish I had taken that coarse. This instuctor is stuck in the 80s, did he have side burns and blue suit to go with 80s theory. The use of micron gauge is strongly reccomended by all manufactors. I use one and it lets me leave the job knowing we got no leaks and system is dry. I use yellow jacket or ritchie and should be approximately 400 microns.
Do it right the first time.
Hard to believe a school would actually teach that. IF you went to school look it up in your refer book.
500 microns is the target. I use a JB but am not all that happy with it.
I graduated in 1987 and we used a thermistor type micron gauge.
Evacuate to 500 microns and isolate.
If the micron gauge rises more than 500 microns (to exceed a gauge reading of 500 + 500 = 1000 microns) at the end of the5 minutes, either a leak is present or an unacceptable level of moisture remains in the circuit.
It should hold at 500 microns. Buy a Thermal Engineering Dual Vacuum Gauge and be happy.
All-American Air Conditioning
Vero Beach, Florida
I like 400
My gauge reads 1000, 600 and 400 in the good section so I always just go to 400 it a little safer. The right number is 500 though.
Do it right the first time.
Well my textbook does say to vacuum it to 500 microns and we did cover that in the classroom, but when we actually did recovery out in the shop we just went off of Hg on our gauges.
Originally Posted by ar_hvac_man
How long should it take to reach 500 microns?
It's not a time issue, it's a measurement issue.
It takes however long it takes.
If I told you 30 minutes and it only took 15 then you've wasted 15 minutes.
If I told you 30 minutes and there was a lot of moisture in the system then you would have never reached it.
Using time to measure a vacuum is like using a ruler to measure weight.
How many inches does it take to make 5 lbs of R-22?
A nonsensical question with no relevant answer.
hg isn't accurate enough. It's like requiring an answer in inches and you can only measure miles.
It's ok with mineral oil as a lubricant, you're doing a triple evac and breaking the vacuum with dry nitrogen. And relying on the filter drier to pick up the rest.
It's not ok when working with POE oil and R-410a.
I use a Yellow Jacket micron gauge that displays the actual number in microns.
Tried the version that just had the bar for different ranges, you could never tell if the system was still pulling a vacuum or was stuck on one reading (a possible leak or moisture.)
Last edited by allan38; 09-13-2008 at 06:06 PM.
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When I started in the industry 35 years ago, nobody every heard of a micron gauge outside of factory design labratory. We used to use the Hg side of the compound gauge as a start point. After that it was a triple-evacuation using R-22 as the moisture absorber between evacuations. It worked okay I guess, least wise we didn't have any great number of non-condensables or premature compressor burn-outs. But today, time is too precious to risk even a small number of issues. So the micron gauge is the only way to go. Most guys will use it for all work involving any opening of the refrigeratioin side of the system. And a good tech plans his work so he's not standing around watching the vacuum pump pull the system down. Get the system tight, leak check with dry nitro and then start the evacuation with the micron guauge on-line. When it gets down into the 300-500 micron range, turn off the pump and the close the valve. The system should stay below 700-800 microns in an ideal world but depending on the size of the system and length of pipes could rise as high as 1,000 microns over several minutes. Anything higher indicates either a leak or moisture in the system. And new vacuum pump oil is required for good results. This is a science, not a guessing game. Good industry practices require the use of expensive equipment and solid knoweldge on the part of the tech. Good service costs significant money for that very reason. Cheap service on the other hand relies on all kinds of shortcuts. Choose accordingly.
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Thermal Engineering makes the best gauge. They have an old style meter that you can tell what is going on. The digital and idiot light ones are no help when you have a problem system.
How low you get the micron count depends on the manufacturers specs AND some info about the system. Small systems w capillary tubes and poe oil should be below 200 microns and triple evacuated. In general any system w poe should be under 500 15 minutes after the pump is shut off.
Mineral oil is more forgiving of moisture. If you can't pull it down then you have a leak or you have water in the system. POE oil will soak up water fast when exposed to air. A lot of it comes down to good technique.
Pulling to a proper micron level depends on what the manufacturer says....Goodman and Amana say 400 microns....three times for R410A. But 500 has always been a good target
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Yellow jacket makes a good one with a replaceable sensor reads from 1 micron to 760000 microns. According to the engineers at yellow jacket a micron reading of 1000 or less indicates a good vacuum and if this reading does not rise over 2000 microns over a period of several hours this indicates no leaks and an acceptable level of molecules in the system.
You cannot remove all the molecules from the system and when a system sits in a vacuum molecules break free in layers, so if you wish to get it to 500 microns and want it to stay there this could take some time especially if you are pulling against a compressor full of refrigerant laden oil.
um, nobody at my work that i know of has a micron gauge, 50 some od techs, maybee il get one lol,
i was brought up by hg/ also,