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Old 05-18-2014, 07:12 AM   #1
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Replacing A/C compressor question


I was taught to- recover the refrigerant down to 5 psi; open the system for as short a time as possible, and only on a dry day; cut out the compressor (and filter/dryer); braze in the new components; pull a vacuum of 30" hg; If it holds 5 minutes, charge the system to 100 psi or so and check for leaks with a halogen detector and/or bubbles. When there are no leaks, finish charging the system. Now I'm told there are more professional procedures. Is my way not complete and safe for the new compressor?

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Old 05-18-2014, 07:36 AM   #2
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Replacing A/C compressor question


Any time I open a line to atmosphere be it compressor, drier or evaporator I remove the schrader cores then connect to condenser and nitrogen flush the system. What you do is is pump the lineset up to around 250 psig (pounds per square inch gauge) and let it settle for a few minutes. This is a two-fer as you will know immediately if you have a leak, as the nitrogen either holds or leaks out, or not and it cleans the lineset.


I do that once, dump the nitrogen via removing hoses from condenser and letting any possible debri fly out through Schrader core openings, install schraders back in and then triple evacuate the entire system.

Nitrogen is your best friend under these circumstances. Remember that old r22 has mineral oil in it and new r410 has polyolester, non compatible or so they say. Best to always use nitrogen imo.

You can google search triple evacuation to find that procedure but basicly 2-3lbs nitrogen, wait ten minutes, dump or vacuum for a few minutes, and repeat twice more.

Once that is all done is when I pull the vacuum to 500 microns. When it comes to microns, 500 is the number to pull down to and it should not settle past 1000 microns, settling meaning once vacuum is over and you turn vac off the microns will rise. We already know we don't have a leak via prior performed nitrogen test so in my opinion it's not worth waiting around to see where the dust settles, so to speak. But that's just me, you do what you feel is best.

Good Luck!

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Old 05-18-2014, 08:15 AM   #3
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Replacing A/C compressor question


There are many versions and ways and every tech has his own. Docs method is very time consuming and when your company charges $100/hr very few customers want to pay a lot extra and some employers expect you to get the job done sooner and quick. Nothing wrong with it though.

Nowadays we use a micron gauge instead of the 30" vacuum. Basically you recover all the refrigerant with a recovery machine until it hits 0 psig or a vacuum. Remove and replace the compressor and drier. Purge the system with nitrogen and pump it up to about 150 psig with nitrogen and wait 5 minutes to see if the pressure drops. If not then you release the nitrogen and pull a 500 micron vacuum and then charge it up with a weighing scale and the appropriate manufacturers charging chart using superheat or subcool. No need to check for leaks if the nitrogen did not drop in pressure. The trick to using a micron gauge is you need to have clean oil in your vacuum pump or it will take forever to get there as the moisture in the oil has to be sucked out too.

You don't want to do the job in the pouring rain but I am sure that in Florida where it is 80% RH humid they do all their work even though the outdoor humidity is high. As long as it is not raining then go ahead. Some times we get caught in the rain and I have finished jobs with a blue plastic tarp over me out of necessity. Unlike baseball we cannot stop everything at the first sign of rain.
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Old 05-18-2014, 09:03 AM   #4
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Replacing A/C compressor question


When I started working on my first monitor top fridge I learned real fast I needed a micron gauge. Using the gauge manifold I couldn't really tell what was going on. I've also read that if you pull below 300 microns or so you risk degassing the oil if there is any present in the system and ruining it.

Being 29.89"hg is 750 microns and and 29.916"hg is 100 microns that is impossible to tell using a vacuum gauge.

If you were working on my system, I'd want you to do a triple evacuation. It's worth the extra time in the long run. The thought of soldering the lines without a nitrogen flow also concerns me a lot. I would never consider such a thing.

FYI, I don't do this for a living, I just work on antique refrigerators as a hobby but I believe the same rules apply.
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Old 05-18-2014, 09:27 AM   #5
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Replacing A/C compressor question


500 microns is the industry standard and we don't have degassing oil problems. Depends on the type of oil perhaps but it is not a problem for us.

There are MANY ways of doing the procedure and there are purist versions, textbook versions and then practical versions that allow a certain amount of time. Your employer may allow you a fixed amount of time and in the real world you will have to develop your own methods to be able to do it in that time. There is no exact right or wrong and if time and $$ were no concern we would do everything according to the textbook or theory.

Here is a link to a Lennox install manual and you can read it and get an idea what a manufacturer wants.
http://www.completeheating.ca/manuals/XC13.pdf
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Old 05-18-2014, 10:02 AM   #6
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Originally Posted by yuri View Post
500 microns is the industry standard and we don't have degassing oil problems. Depends on the type of oil perhaps but it is not a problem for us.

There are MANY ways of doing the procedure and there are purist versions, textbook versions and then practical versions that allow a certain amount of time. Your employer may allow you a fixed amount of time and in the real world you will have to develop your own methods to be able to do it in that time. There is no exact right or wrong and if time and $$ were no concern we would do everything according to the textbook or theory.

Here is a link to a Lennox install manual and you can read it and get an idea what a manufacturer wants.
http://www.completeheating.ca/manuals/XC13.pdf

yuri, my point was you must use a micron gauge when vacuuming otherwise you could either not pull a deep enough vacuum, or you could degas the motor oil.

One of the places I have seen this is on JB's website.

http://www.jbind.com/technical/faq-micron-gauges.aspx
"
4. I purchased a new micron gauge. How low of a vacuum should I pull?

Some manufacturers have a micron range that they want their system pulled down to, so therefore, JB can only suggest a micron reading. Our suggestion is to pull a system down to 250-300 microns only if you are also pulling a vacuum on the compressor. Going below 250 microns, you will start degassing the oil in the compressor and it will not be the same lubricating oil as it was originally. The oil will only degass and will not suck up into the vacuum pump."

If a hobbyist such as my self was willing to spend money on a quality micron gauge because it's a necessity I would think any professional should do the same. No?
I went with a Yellow Jacket 69086. It's not the best, but its far from the worst.


I do not consider a micron gauge, or flowing nitrogen as optional. I have a feeling you have the same opinion so I think overall I agree with you 100%.
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Old 05-18-2014, 10:12 AM   #7
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Replacing A/C compressor question


Pulling a vacuum just inches from the brazed joints is pulling refrigerant from the rest of the system past the effected area, theoretically pulling all air and nitrogen from the system. I have brazed joints with and without nitrogen, cut them out, and examined them, and I agree. Without nitrogen there is a thin layer of loose soot. My coworker vacillates on the subject so we haven't added that to our regimen. We bought a Testo micron gage and a manifold set just for evacuating a system. We never got the vacuum below 9000 microns and when valved off, it shot up immediately. We switched back to our digital set and it held at 600 microns. Does anyone think that the original method I described puts the compressor at risk? (I always test the refrigerant pulled out for acid, and smell it for a clean refrigerant smell- no burnouts).
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Old 05-18-2014, 12:12 PM   #8
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Replacing A/C compressor question


Your original way is an EPA violation.

Small appliance must be recovered to 4" of vacuum.
Type II containing less then 200 pounds of R22 charge must be recovered to 0", more then 200 pounds, 10".
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Old 05-18-2014, 04:16 PM   #9
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Replacing A/C compressor question


In practical terms, I would be releasing more refrigerant to the atmosphere if I used 1% refrigerant with nitrogen up to only 50 psi to pressure test it.
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Old 05-18-2014, 04:17 PM   #10
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Replacing A/C compressor question


That's 10% refrigerant...

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