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Pressure Testing Mitsubishi 4 zone Mini Split System

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sparkySF
sparkySF Member Posts: 6
in A-C, Heat Pumps & Refrigeration

Hi there,
I just installed a condenser (Mitsubishi MXZ-4C36NA3 uses R410A) and 4 ceiling cassettes (MLZ-KP09NA2). Now I'd like to run a nitrogen pressure test and I'm wondering about what max pressure to use. The condenser shows on the name plate: Design Pressures 601psig on the high side and 320 psig on the low side. I assume the "high side" refers to the high-pressure liquid line and the "low side" to the suction or gas line. The condenser has only one service port which is on the gas side. So here are my question:
1. What max pressure can I use for the pressure test given that the gas side ("low side") has a design pressure of 320 psig?

2. Does a successful pressure test (at the correct pressure) imply that the gas and the liquid side have been tested, i.e. all line sets as well as the piping inside the 4 different ceiling cassettes and condenser?

3. Once the nitrogen pressure test is completed and no leak is detected is it possible that the vacuum pump might create a leak?

Thanks for your time to read this and hopefully give me some guidance. I appreciate it.

Comments

  • ratio
    ratio Member Posts: 4,202

    • 1) You're always ok to use the low side test pressure. Mitsubishi VRF systems spec the high side for all their field piping, FWIW. I'd use 250# or 300#, at least overnight, on a multi split. There's lots of joints that could be leaking. Mind the temperature changes from day to day.

    2) It implies that but isn't a 100% guarantee. I've had some piping that held pressure but not vacuum, but that's fairly rare.

    3) No, but a vacuum test is part of it.

    A pressure test followed by a vacuum test is the procedure. Test to whatever, 300# is fine, if that hold then you go to a vacuum test, it needs to settle down and hold under 500µ without moving, for 5-10 minutes.

  • pecmsg
    pecmsg Member Posts: 6,881
    edited January 19

    On there R-410A systems Mitsubishi wants 600#'s standing pressure of leak checking. I only get to 500#'s with my regulator.

  • sparkySF
    sparkySF Member Posts: 6

    Thanks guys.

    @pecmsg Where do you get your 600#s from? The installation manual doesn't talk about pressure testing and your 600 seems to go against the info of the name plate (provided I interpret that information correctly).

  • pecmsg
    pecmsg Member Posts: 6,881

    For Mitsubishi 600 psi pressure testing, it is generally recommended to test to 600 psi for R410A systems, as this helps ensure there are no leaks after installation.

  • pecmsg
    pecmsg Member Posts: 6,881
    edited January 19

    The 600 # pressure test is just the first leak check.

    The second is pulling a vacuum to at least 500 microns and having it hold below 750 - 1000 for several hours. This may require several attempts.

  • ratio
    ratio Member Posts: 4,202

    @sparkySF, the 600# (Actually a hair higher due to the SI conversion) is from a lot of their other other IOMs. I remember it in particular from the VRF instructions, as documenting it is part of the extended warranty process; but I use 250-300# for mini & multi splits as it's not going to make a significant difference.

    The vacuum test is far more important, not only from a leak perspective but from a cleanliness & dehydration perspective. Most mini splits don't use hygroscopic oils and don't have filter-dryers, just very fine mesh screens, so any moisture that remains in the system will stay in play until it has a chance to eat it's way out.

  • sparkySF
    sparkySF Member Posts: 6

    So I did end up calling Mitsubishi regarding my question (mainly #1). I was told to ignore what's on the name plate and use a test pressure between 400 psig and 500 psig. He did not explain to me how he got those numbers. Regarding vacuum he said I should draw a vacuum 3 times each time pulling a vacuum deeper than the previous one before releasing it. I guess that might help with drawing out any water. Thought I share so people are aware.

  • mattmia2
    mattmia2 Member Posts: 15,992

    triple evacuation is an old method from before micron vacuum gauges were common. If you can pull it down to spec and hold it for the specified time you are good.

  • sparkySF
    sparkySF Member Posts: 6

    Interesting background info.

    Thanks for that color mattmia2.

  • pecmsg
    pecmsg Member Posts: 6,881

    You will need a Micron gauge.

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