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I'm installing a Bosch Climate 5000 series 3-zone mini split system in my house. This is my third mini-split installation (although I had an HVAC guy deal with the plumbing on the first one).

HVAC training videos online go through a thorough procedure of first pressure-testing the system with nitrogen at ~300 psi, then drawing a vacuum and testing that the vacuum holds. For example, one video describes a thorough pressure test, while another describes a thorough vacuum pull with very specific steps (remove Schrader valves & use a large hose with direct connection for speed, test pressure at far end, etc.).

The last LG system I did, I only did the vacuum draw (no pressure test). A year later, it still seems to be working fine.

The Bosch installation manuals say nothing of a nitrogen pressure test, and just shows a compound gauge and “recommends” using a micron gauge. The valves on the compressor don’t allow for placing the gauge at the far end of the line. In all, it seems like a very minimalist test procedure.

In fact, the instructions say that if the vacuum test fails, to go to the “Gas Leak Checks” section, which instructs to apply soapy water to joints and to look for bubbles. Strictly following this skips over the steps where you open the valves to fill the system with refrigerant, so there wouldn’t be any bubbles even if a joint was leaky.

How important is it to go above and beyond the manufacturer’s recommendations? Is there any reason not to (e.g. potentially damaging the system with a pressure test)?

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    Well, you certainly should not fill a leaky system with refrigerant to look for bubbles, either, as you'll be leaking refrigerant. So you obviously are going to want to pressurize with nitrogen for that step, if needed. FWIW, The folks (pros) that installed mine (Different brand) definitely pressure tested and then vacuum tested. The system needs to hold refrigerant pressure, and some leak modes are more likely to show up with pressure than with vacuum.
    – Ecnerwal
    Commented Oct 11, 2022 at 16:22

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Usually a manufacturer's instructions is what you need to go by.

Not following or doing other steps becomes money out of your pocket.

If not sure of the instructions ask the manufacturer, sometimes they do make mistakes or write them so they might not be understood completely.

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    "make mistakes" considering that if the vacuum doesn't hold, the instructions skip the user to the "soapy water & look for bubbles pressure test" step, it does sound like this may be the case here. (You're not going to have bubbles from soapy water when drawing a vacuum.)
    – FreeMan
    Commented Oct 11, 2022 at 13:12
  • Oh, you will - you won't see them as they'll be inside the pipes/fittings, contaminating your system. Extra-good.
    – Ecnerwal
    Commented Oct 11, 2022 at 17:01

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