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Evacuation of small ac systems

I would like to hear views on best way to evacuate using micron gauges, hoses etc. I have always used gauge sets and standard hoses.sometimes good results, sonetimes not. Trying to figure out best ways as i have had alot of different views using special vacum hoses, copper hoses etc.thx


  • Empire_2Empire_2 Member Posts: 2,343
    edited June 2015
    In general most pumps ( not all) usually evacuate to 5 CFM. Better pumps can do 8cfm. Typically small systems or any system for that matter is all based on how good your equipment is! If your hoses are in question, nothing is more stressful that thinking why is my micron gauge coming up when I know all joint's are good......! Ever been there? Once you start questioning your manifold, hoses, seals, etc... It can drive you crazy. All I can say is have quality equipment that has been tested on at least a monthly basis because in fact when you don't want it to fail, something usually does and that's where you start asking yourself....................Is it my hoses, or do I have a leak at the seal of the gauges, ,perhaps the pump is no up to spec/ etc...... See how crazy it can be?
    You are not the first to ask this seemingly easy question, and will never be the last. I ask myself every time, "Is everything set to perform this procedure"!!! If there is a leak, I ask myself, since I know the system is tight, It must be the accessories or is it the leak in the system that I just convinced myself that there was no problem with.......:-) Just my .02

    Bob Bona_4
  • Paul_69Paul_69 Member Posts: 247
    Thanks empirr
  • JUGHNEJUGHNE Member Posts: 6,923
    How things change! My first AC's install were for my duplex rental property. In 1983 the "norm" was to use R-22 from the tank and flush the air out of your line-set, alternate liquid and suction line flushing and vent as rapid as possible. (Don't need no stinking vacuum pump :D ). Actually didn't need a gauge set, just one hose. I believe the saving grace was adding a LLFD and the fact that all connections were flare fitting; no redneck torching with 50/50 solder. 1/4" & 5/8" od ACR for 1.25 tons.

    These AC units are running today 32 years later! I have changed the inside units/air handlers recently and did use all the proper methods.

    But of course this was R-22, not 410A with it's little girl oil which won't take any abuse at all.

    So today my standard procedure is: (after investing a couple thousand years ago) Remove valve cores, connect fittings (also LLFD) with 15% silver with N2 flowing, flush with N2, Pressurize with N2 to maybe 500PSI for at least an hour, maybe more, triple vac at least using digital vac gauge, flush with N2 between. Then before the last vac while system is under N2 pressure (10 PSI0) reinstall the cores and do final vac. Don't put quick connectors on for vac pump operation. Get system down to as low as possible and holding. Then crack the liquid valve to get system pressure up to 10 + PSI and close valve. Remove hoses and install quick connectors. Then open valves completely.(Don't like to freeze fingers with 410A and don't trust quick connects for vac operation..sounds like a real ceremony, but today for me it is just the standard procedure and doesn't require that much thought/effort....from the first flow of N2 gas the system never sees air again.

    There are plenty of other things to do while this process is going on, wiring..sealing duct...etc. The only thing I really pay attention to is if the vac pump quits for any reason at all is to isolate it from the system as quick as possible. Vac pump oil pulled into a 410A system would be what I imagine a real dilemma.

    I might test the some of the hose fitting connections by closing the hi & low valves on the manifold set and seeing what the vac pump will do pulling on the digital vac gauge only. As for the other connections you just get a feel of something wrong if the microns rise rapidly with vac pump valve off. The 500PSI pressure test pretty well confirms there are no leaks.
  • John Mills_5John Mills_5 Member Posts: 935
    Look into the Appion kit MGABAS which is a core removal tool that you hook to one of the ports on the unit. The kit comes with a 1/2" hose that you hook to your vacuum pump. Then put your micron gauge on the other port so you are reading your vacuum at the other side of the unit. Standard colored 1/4" hoses don't pull a vacuum well. Black hoses are for vacuuming and the 1/2" hose lets your 5 CFM actually pull 5 CFM, not 1/2 CFM. After 1 installer bought the kit and showed the others how fast it was, several more have as well.
  • ChrisJChrisJ Member Posts: 11,003
    edited July 2015
    I tried using the gauge off of my manifold set and that didn't work at all for vacuuming. I had no idea if I was down low enough so I bought a decent micron gauge.

    Hoses are always said to be a no no but I get away with it using a short length. A length of soft copper would work far better I'm sure. I always use fresh vacuum pump oil and leave the ballast valve open until I get below 1000 microns or so.

    I install my gauge sensor as shown in this picture to try and keep oil from getting in it. If oil gets in it, it's toast and need to be cleaned. This is very important with these gauges. I also keep it installed as close to the unit being vacuumed as possible, not back at the pump.

    I also heat the unit being vacuumed with sometimes lamps and often a heat gun. I'll also often do nitrogen purges were I fill the unit with nitrogen and then pull it down again. These machines do not have a drier (at least not yet anyway) and the refrigerant breaks down from moisture so a dry system is extremely important.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • LanceLance Member Posts: 142
    A good vacuum pump, fresh clean vacuum oil, place a great micron gauge as close as possible to what needs to be tested so it can be isolated from as many connections as possible including the pump. 400 microns is a standard we evacuate to but we can go as low as 200 but we do not need to unless we work on special equip. 400-500 microns will make sure moisture boils off even in low temperatures (check chart for specifics). Speed is important for large systems, look for vacuum pumps rated 7CFM or more. But that is meaningless unless the Schrader cores ( if present) are not removed during evacuation. Must have check valve in pump to prevent vacuum oil from being pulled into system if power shuts off accidentally. ( always break the vacuum before turning off pump). Once vacuum limit is achieved isolate all so micron gauge only reads the system to determine moisture or tightness. If good, break vacuum with dry pumped nitrogen if needed or the proper refrigerant. With 410A's oil some prefer medical dry pumped nitrogen to insure no moisture is left in the system. Just remember if a manifold vacuum gauge reads 28" vac it could just as well be 26". Gauges are notoriously inaccurate at both ends of their scale.
    400 microns = about .016" mercury on your gauge.
    I am told it is best to have a set of gauges for r-22, r-12, R 410a. Main reason we all got new hose and sets for 410a is the gauge reading and the fact the pressures are greater and so the hoses had to be rated for higher pressures. And never should oil mix between systems. Oil in hoses is not always easy to clean out. The oil flows with the refrigerant.
    Best advice is from the factory.
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