Bosch Mini Split Installation: Air Handler is pressurized from the factory

mcho · April 2019

I received a BOSCH mini split 18000 BTU brand new in the box from a friend. I studied the installation manual and watched the online DIY videos. Seemed pretty straight forward, the hardest part getting a good seal on the connections, doing a nitrogen leak test, and drawing an adequate vacuum. But as a nuclear engineer all within my capabilities. Heck, I teach how to do swage lock and other copper tube connections at work.

Imagine my surprise when I went to remove the caps on the line set from the air handler to attach the line set from the outdoor unit. The air handler was highly pressurized! As soon as I heard the hissing I immediately re-tightened the cap. What the gas was I don't know. There was no odor (I did not sniff it and went out of my way not to breath it!!). My understanding was that the R410a precharge was in the outdoor unit,

What does this mean? There is no mention of this in the installation manual or any of the online videos. The online videos are for various other brands including popular Japanese brands that look absolutely identical to the Bosch (the internal parts not the exterior). Not one mention of the air handler being pressurized. No results from Google searches.

hvacfreak2 · April 2019

Common industry practice from a manufacturer would be to pressurize the unit with an inert gas to prevent it from filling with atmosphere , at least until the time of installation. It is also a good indicator that the unit is tight ( in the event that the system does not hold during a pressure test I would not start looking for a leak at this unit ) . It is also required for the installer to pressurize the field connected portion with an inert gas and hold for a period of time ( determined by manufacturer ).

mcho · April 2019

Thanks havacfreak2. Thats a relief! I was hoping that was the case. OK I guess I can go back to installing the unit now but I will start at the outdoor unit so I leave the air handler exposed to the atmosphere the smallest amount of time. I already have the line set in place but I have to cut and flare at the outdoor unit so that will take some time,

hvacfreak2 · April 2019

I just use tape to cover the end of the tube if the tube needs to sit open for awhile. Clean and dry is the goal for ACR piping , I wish all manufactures shipped indoor coils under pressure ( they did for awhile but it can be either way these days ).

JUGHNE · April 2019

I have saved all the plastic caps from ACR coils over the years.
They push on nicely and if have to stay outside for awhile a wrap of black tape keeps them secure.
I have all the black push in plugs also.

Some call me a pack rat/hoarder....

mikeg2015 · April 2019

Pressurized with nitrogen to prevent moisture from getting in. Also lets the tech know that after it’s journey from factory, to warehouse to distributor, to LTL shipping, tossing it around in the shop, truck, up stairs and hanging the unit, the coils still hold pressure.

Couple small tips. We use soap to check all connection (brazed or flared) when it’s pressurized. We always blow out the line set before making the last connection. The flared fitting often need ot be torqued more than the “specs” listed. We used ot use a torque wrench but got tired of call backs after units lost pressure. But too hard and you can strip the threads and no way to realistically replace a service valve. You can hopefully claim warranty. 14ga Outdoor speaker wire is a lot cheaper than what is sold as “mini split communication cable) and probably the same thing.

Been installing about 1 mini split for every 3 conventional systems lately. Lots of all electric homes around here so these replace baseboard and window units in many cases.

Bosch Mini Split Installation: Air Handler is pressurized from the factory

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