As and HVAC student reading a book from the field I learned about the concept of triple evacuation today. Im a little confused as to why this is necessary. It seems to me that you evacuate once and the system should be good but letting some trace refrigerant back in and evacuating again and then repeating it yet again? What is the purpose? Im sure there are plenty good reasons out there and as a dumb student I'd love to know them.
triple evac was before the epa cert/micron days kicked in when you burped the vac with the systems freon then revac'd it...now the microns below 5000 are considerd moisture and as it dries up you start passing thru into 4000,3000,2000 and 1000 microns mint vacs are 500-250 micron range and let it sit for 4 hours/if you can't get below 5000 microns at the start there is a leak.........
Long, long ago...
Triple vac and purge with refrigerant was back in the day when we blew out condensers with R-12 (legally OK).
How old is that textbook?
Experience is what you have an hour after you need it.
It is probably subtitled: "Working with GE air conditioners."
Originally Posted by baub
[Avatar photo from a Florida training accident. Everyone walked away.]
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Me thinks GE air conditioners were fantastic.
If somewhat difficult to service.
No one I know triple evacs any more.
Nitrogen pressure test , release nitrogen , evacuate with micron gauge.
Theory was that the addition of refrigerant to an evacuated system would let the refrigerant help carry contaminents out of the system during second and third evacuation. Kinda like a "Purge". Not practiced these days because of CFC restrictions.
One way to outthink people is to make them think you think. They'll think you're not really thinking what you're trying to get them to think you think...........
The theory of reducing contaminants by breaking the vacuum with refrigerant is still sound, just illegal.
Originally Posted by uniservice
Even under a deep micron vacuum, there IS still vapor in the system. By breaking the vacuum with refrigerant, you replaced the air or nitrogen with refrigerant, thus reducing the amount of remaining contaminants.
This may be splitting hairs.
I normally just pull deep vacuum and recharge as is typical procedure.
Yes they were. Replaced one 6 years ago. Side discharge cfm, gigantic caps.
Originally Posted by AiResearch
Early 70's i think.
Some Talk, Some Do
"keeping condensing pressures low and evaporator pressures high"
Comfort is my goal
The book I was reading is:
Refrigeration & Air Conditioning Technology 4th Edition
by Whitman * Johnson * Tomczyk
Not exactly the most current issue of this book but still tons of good knowledge. Thanks to you guys for all the help.
Our company's procedure is tripple evacuate (even R-22 systems), we don't use refrigerant, we use nytrogen. We have very few call backs due to leaks (the few we have, I would guess, someone cut a corner somewhere).
Mitsubishi City-Multi requires " Triple Evac. " using nitrogen.
I took my cfc certification a long time ago ( 1993 I think ). At that time it was legal to vent refrigerant for the purpose of " dehydration and leak testing " if I'm remembering correctly.
I installed a ten ton Aaon split system 2 weeks ago and did a triple evacuation using nitrogen and the results were dramatic ( from the first pump down versus the second ). Using an Appion TEZ-8 pump and 2 micron gauges ( one analog and one digital ) ...the initial evac. was 500 ( pump running ). Broke vacuum to 30 psi nitrogen , bleed out of low side of system to 5 psi. The next evac went down to 200 microns ( pump running ) in a much shorter time than the first. System settled at 350 microns for an hour ( both gauges agreed , I called it good ).
I can assure you that using refrigerant for this process will reduce evacuation time by at least 1/2 ( if I'm remembering correctly ).
Last edited by tech45; 04-22-2011 at 11:00 PM.
Pretty sure the text books state that dry nitrogen has a higher moisture absorbtion than a refrigerant , however some refrigerants are great solvents for removing other contaminants. Just depends on the situation. Cant go wrong with nitrogen and a micron gauge IMO.
One could start a whole new thread about GE refrigerating equipment!!!
Originally Posted by ACFIXR
The domestic fridge would run forever and ever and ever.
Neat thing about that company is they made EVERYTHING in the unit. Right down to the wire.
And their hermetic compressors were workers tougher than a Mack truck.
Man ive seen those things run under the worst conditions for weeks...
They really put the good metals in there..
(sorry for the sidetrack guys)
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