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  1. #1
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    Micron gauge jumps from 200 micro to ~770 micro

    This is my first post to HVAC-TALK. I have used this several times when problem solving an issue. Thanks to everyone who supports making possible this valuable source of information.

    I am pulling vacuum on a new split system. The line-set was braised with Nitrogen in the system and pressure tested at low side rate of 250 psi. I am able to pull the vacuum down to ~200 microns. Immediately after isolating the system and turning off the vacuum pump, the gauge climbs to ~770 microns. I will list set up first followed by my process and what I tried to remedy the issue. Thanks in advance for any ideas anyone here can offer as to what is at issue.

    Set-up--

    1. Low side service connection
    - Valve core removed
    - Two (2) Appion VCRT
    -- First VCRT connects to vacuum pump via 1/2" x 6' vacuum hose with 3/8" FL and 1/4" FL ends; valve core is removed from side port
    -- Second VCRT connects to side port of first VCRT; CPS VG200 vacuum gauge connects to end of this VCRT
    2. Liquid side service connection
    - Valve core removed
    - One (1) Appion VCRT connected to service port; 1/4" hose from VCRT to pump
    3. Pump is Robinair, model 15601 6 CFM Vacuum Pump
    4. Line set length is ~74'; ODU located on roof ~35' above IDU
    5. System is Bryant furnace with split AC system

    Process--
    1. Pull vacuum-- Initial vacuum to ~200 microns required ~15-20 minutes
    2. Isolate system by closing VCRT ball valves connected directly to service ports
    3. Gauge jumped to ~880 microns
    4. Opened gas ballast on pump; ran pump again; tested
    5. Did this a few more times; each test resulted in same outcome
    6. Broke vacuum with nitrogen; waited 30 minutes; pulled vacuum; gauge jumped
    7. I estimate I pulled the vacuum down to ~200 microns at least 6-8 more times before calling it for the day.

    Is moisture causing the issue? Do I have a leak...seem unlikely as the micron gauge parks itself after the initial climb out of deep vacuum. I also will add that the final reading, while isolating the system, read ~680 microns at one test but 740-770 microns was typically where the gauge stopped.

    Thanks for reading and for any help readers out there may be able to offer.

  2. #2
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    Personally I would call it good, if it doesn’t climb above 1000.


    Sent from my iPhone using Tapatalk

  3. #3
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    Have you test your vacuum set up? is the change being caused by your set up or by the system. Put your vacuum gauge on the liquid line, farthest point away from vacuum source, try it again.

  4. #4
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    Thread Starter
    Quote Originally Posted by Answer-Man View Post
    Have you test your vacuum set up? is the change being caused by your set up or by the system. Put your vacuum gauge on the liquid line, farthest point away from vacuum source, try it again.
    By using three Appion VCRTs, there is very little that can go wrong with the vacuum set up outside of leaks at threaded connections. And I checked these several times. Also, the fact that the vacuum reading settles at a number and does not move tells me the set up is not the issue. Also, I am pulling a vacuum on the suction and liquid lines...system is equipped with TXV and this method improves vacuum as it does not pull across the metering device. The vacuum gauge is taking a reading on the suction line; setting it up on the liquid line seems like I would get the same results.

  5. #5
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    So in general when you have what you have explained. Vacuum becomes less then stops when the vacuum pump is isolated, what is the cause?

    Not all of air and non-condensable have been removed

    If you are certain all air and non-condensable have been removed then it is your vacuum pump set up

    So what is the cause?

  6. #6
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    Thread Starter
    Correct- I am able to pull vacuum to 200 microns, slightly less. As soon as I turn the ball-valves on each of the VCRTs connected to suction and liquid service ports, the vacuum reading climbs to approx. 800 microns and stops. I think this points to air or non-condensables in the system. I am also new to working with refrigerant and felt it best to ask people who may have experienced a similar issue.

    I am not certain all air and non-condensables have been removed. So, perhaps I simply need to run my pump longer? A couple more sweeps with nitrogen?

    Also, the air handler was running in fan only mode so that air was blowing across the coil. I understand this can help prevent moisture from freezing while vacuuming a system.

  7. #7
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    I have read and re-read what you have written several times. This is a new system, New evap which had a notrigen blanket, 150 feet of line set which should have had a nitrogen purge and capped, new condensing unit which still has the service valve closed and some refrigerant from the factory in the condensing unit. With respect to vacuum change in elevation should no impact on the ability to pull a vacuum

    With the micron gauge 3 feet off the vacuum pump the vacuum idicated will appear low quickly. Good practice says the micron gauge should be placed at the farthest point from the vacuum pump

    A couple more questions
    How long have you ran the vacuum pump before checking pressure?
    What size unit is being installed (small volume or large volume is being evacuated)?
    Are you utilizing a triple evacuation method?
    Each time you have checked the micron reading have you broken vacuum with nitrogen or simply restarted the vauum pump.

  8. #8
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    Thread Starter
    Quote Originally Posted by Answer-Man View Post
    I have read and re-read what you have written several times. This is a new system, New evap which had a notrigen blanket, 150 feet of line set which should have had a nitrogen purge and capped, new condensing unit which still has the service valve closed and some refrigerant from the factory in the condensing unit. With respect to vacuum change in elevation should no impact on the ability to pull a vacuum

    With the micron gauge 3 feet off the vacuum pump the vacuum idicated will appear low quickly. Good practice says the micron gauge should be placed at the farthest point from the vacuum pump

    A couple more questions
    How long have you ran the vacuum pump before checking pressure?
    What size unit is being installed (small volume or large volume is being evacuated)?
    Are you utilizing a triple evacuation method?
    Each time you have checked the micron reading have you broken vacuum with nitrogen or simply restarted the vauum pump.

    Answer-Man,

    Initial comments are correct. Thanks for pointing out that elevation change should not affect vacuum.

    Thanks for pointing out locating micron gauge farthest from pump as possible. The 1/2" hose connected to the suction side is 6' long; this is where my micron gauge TEES into the the VCRT.

    Replies to your questions--
    How long have you ran the vacuum pump before checking pressure?
    -- Approximately 15 minutes on first pull; 20 minutes on later attempts
    What size unit is being installed (small volume or large volume is being evacuated)?
    -- 5/8" suction; 3/8" liquid lines
    Are you utilizing a triple evacuation method?
    -- I plan to. I thought I should first prove I am able to pull a deep vacuum prior to beginning triple evacuation and sweeping with nitrogen. I did sweep with nitrogen once. When I vacuumed down the system after the nitrogen sweep (30 minutes at approx. 15psi), the final, system isolated, vacuum reading was the same as before.
    Each time you have checked the micron reading have you broken vacuum with nitrogen or simply restarted the vauum pump
    -- Simply restarted the vacuum pump on all but one as described above. I also opened the gas ballast on the pump after restarts...I understand this can help remove moisture more quickly.

    Perhaps I simply need to run the pump longer combined with triple evacuation now?

  9. #9
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    In your original post you stated you pulled a vacuum to 200 from about 800 6 or 8 times. What I get is you used nitrogen 1 time so you have a fair amount of vacuum pump run time on the system, so you should have seen the micron level improving. Just a suggestion. Yes pulling a vacuum from the low side to high side is a good practice but I like to use a tee on the vacuum pump itself with an isolation valve for both. This way I can separate the High side from the pump, then meassure the micron value at the furthest point. So if you are configured with the valve core tool so you can do that, Start your vacuum pump when you get down to about 200 again, simply isolate the high side from the vacuum pump so you are reading the vacuum with the Vacuum pump running through the evap coil and 150 ft of line.

    I do not use the apion system but I do utilize large bore lines, hoses and isolation valves so I can do as I just said ans well as purge with Nitrogen and add refrigerant when it is time without breaking connections

    Last question when was the last time you changed the oil in the vacuum pump?

  10. #10
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    Thread Starter
    Quote Originally Posted by Answer-Man View Post
    In your original post you stated you pulled a vacuum to 200 from about 800 6 or 8 times. What I get is you used nitrogen 1 time so you have a fair amount of vacuum pump run time on the system, so you should have seen the micron level improving. Just a suggestion. Yes pulling a vacuum from the low side to high side is a good practice but I like to use a tee on the vacuum pump itself with an isolation valve for both. This way I can separate the High side from the pump, then meassure the micron value at the furthest point. So if you are configured with the valve core tool so you can do that, Start your vacuum pump when you get down to about 200 again, simply isolate the high side from the vacuum pump so you are reading the vacuum with the Vacuum pump running through the evap coil and 150 ft of line.

    I do not use the apion system but I do utilize large bore lines, hoses and isolation valves so I can do as I just said ans well as purge with Nitrogen and add refrigerant when it is time without breaking connections

    Last question when was the last time you changed the oil in the vacuum pump?

    Oil in vacuum pump was new


    As I read your recommendations:
    -- move the vacuum gauge to TEE into the VCRT located on the liquid line
    -- Pull vacuum with high/low open to ~200 microns
    -- Isolate high side leaving vacuum pump running and observe changes in vacuum reading...this method allows me to observe vacuum readings with micron gauge as far from pump as possible.

    I will also plan to perform nitrogen sweeps and run the pump longer than I did before. It seems very unlikely there is a leak in the system.

  11. #11
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    Good luck

  12. #12
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    Is your setup new? Is so, the hoses will off gas for a while. You can set them up on a pump and pull a vacuum overnight. That should take care of most of the off gas. Otherwise, run a longer vacuum. Jim Bergman has a video about how long you should run a vacuum. I think it’s on the tru tech tools site. He explains that just pulling down to 500 or 250 or whatever doesn’t guarantee you’ve removed the moisture it just tells you that the water will be boiling. That’s what the decay test is for. Best of luck and good for you for working to improve yourself.

  13. #13
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    Quote Originally Posted by Achso017 View Post
    Is your setup new? Is so, the hoses will off gas for a while. You can set them up on a pump and pull a vacuum overnight. That should take care of most of the off gas. Otherwise, run a longer vacuum. Jim Bergman has a video about how long you should run a vacuum. I think it’s on the tru tech tools site. He explains that just pulling down to 500 or 250 or whatever doesn’t guarantee you’ve removed the moisture it just tells you that the water will be boiling. That’s what the decay test is for. Best of luck and good for you for working to improve yourself.
    Yes. My setup is new. Good to know the hoses will off gas for a while. I am able to isolate my hoses from the vacuum using the VCRTs connected at low/high side service ports. It sounds like a simply need to run a longer vacuum. I appreciate you replying to my post. Thanks!

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