Vacuum Meter Question

[peanut2004]

Hi All,

  I just bought a Supco vacuum meter.  I have now used it on three different systems and this is what happened..

1)  System 1..Ductless 410a 9000btu..Found evidence of oil around the service valves...Pressurized to 125 psig..soap and water bubble test...Nothing.  Held pressure fine for 1hr.. Connected my vacuum pump and my new vacuum gage to the high side line off my gauges..  Vacuumed for 1hr it pulled down to about 500 microns, I turned off and isolated the vacuum pump. It climbs slowly to 1100 microns, then it started to go back down and seem to settle in at 850 microns??

2) System 2...Same house, same unit different floor. Almost the same outcome. Called the manufacturer about the service valves, Put leak lock on all flare and service valve caps..

3) System 3....Ductless 410a 18000. New install.. Vacuumed down to 450 microns 1hr..Turned off pump, isolated it.. Slowly climbs to around 1100 and settled in. I had also checked for leaks 125 psig nitrogen and soap and water..

Is this normal??  I have a 6cfm vacuum pump.  The readings were leading me to believe there was a leak. So I re-pressurized re-checked for leaks and every thing held??

Please let me know before it goes in the garbage....My gauges and hoses are also new...I just read something about off gases from new hoses...Can someone confirm this is a problem

Thanks

[Admin]

I use Yellow Jacket equipment.  Check out their SuperEvac™ Evacuation Systems I, II and III - Here
Order a #69067 ball valve to attach to the micron gauge sensor.  Keeping the ball valve closed during the pump startup can prevent damage to the sensor.  Also near the end of the evacuation you can turn the ball valve half closed for a couple of minutes.  The gas that is normally trapped between the valve seal and body may be the cause of your rise in microns.

You're right about the rubber hoses, some molecules will be sucked out of them.  Metal hoses are available.  I can get to below 300 microns on a new install, and I don't worry about a rise in microns after I isolate the pump from the system.  It is perfectly normal to see a rise in microns.  If you want to monitor the rise in microns, be patient and let it stabilize.

I remove my Schrader core before I weld, then I pump 150 psi of nitrogen into the system using an old manifold for 30 minutes.  If there's no drop in pressure I release the nitrogen and disconnect my manifold.  Now I install the vacuum/charge valve tool to both my low and high side ports.  Evacuating from both sides with no schrader cores will save you alot of time.  I hook up the SuperEvac gauge and hoses to my vacuum/schrader valve tools and pump.  I open the blank off on the pump and make sure the ball valve at the sensor is closed.  I now start the pump.  I open the valves on the vacuum/charge valve tools, then the valves on my SuperEvac tool, lastly the ball valve protecting my sensor.

I included a couple of documents I scanned from Yellow Jacket, definitely worth the read.