Mr slim mxz-4a36na evac question?

[wengr]

Hello, I have to evecuate a newly installed mitsubishi mr slim mxz-4a36na quad zone mini split. it's pre charged with r410a. I have my vacuum pump connected to the schrader valve port on the gas stop valve as per the intructions, but I believe the system is still closed as it goes down to 30 inches in about a minute. all I am evacuating is the manifold and hoses. however if I open the allen keyed valve where I'm connected, then the charge will spread. how to evacuate, and then release the charge? I did'nt see a forum for dumb questions so I put it here. thanks in advance, greg

[frank]

Greg

It sounds like you have connected your gauge set (manifold) correctly but are only evacuating the line between the vac pump and the gauge set.

Open the valves on the gauge set to allow the vac pump to 'see' the line set.

Once you have a good vacuum you can then stop the vac pump and open the allen key valves.

[monkey spanners]

Sounds like schreader core isn't being deprested properly, are you using a 5/16 to 1/4 adaptor? Might be worth screwing the core depresor out of the gauge line a bit to see.
I've just bought a core depressor tap made by robinair to try and prevent this problem, i expect yellow jacket make something similar too.

[wengr]

Greg

It sounds like you have connected your gauge set (manifold) correctly but are only evacuating the line between the vac pump and the gauge set.
Hello Frank and thanks for the reply. I did triple check the manifold and it's set correctly. I am putting vacuum to the schraeder on the units gas stop valve. if it's pulling beyond that I can't say.

[wengr]

Sounds like schreader core isn't being deprested properly, are you using a 5/16 to 1/4 adaptor? Might be worth screwing the core depresor out of the gauge line a bit to see.
I've just bought a core depressor tap made by robinair to try and prevent this problem, i expect yellow jacket make something similar too.Spanners thanks for the reply. I am not using a 5/16 adapter kit as this mitsubishi unit still uses 1/4. That's a good idea about the core depressor, however the depressors in my hoses do not extract, they just spin at the same depth. they do however seem to function correctly.

[wengr]

What I could really use is to know if there is anything non standard about the gas valve - service port assembly on this particular mitsubishi unit?

[monkey spanners]

I would expect the valves to work the same as on other mini splits, have you got one of those core changing tools that you can use under pressure? Might be worth taking the core out and vacing, then just break the vacuum up to a few psi, then put a new core in and release the charge into the pipework.

I had a counter fridge i spent ages vacing out last week, before i realised that despite the core being ok when i pressure tested for leaks, the vacuum seemed to suck it shut. Still all my hand tools are nice and clean now as i got bored waiting the second time...

[wengr]

It seems that there is nothing unusual about the gas stop valve. this was my first mini split so I thought I'd ask, as better safe than sorry. turns out the problem was not at the schreader. after trying to pull a vac for awhile, I disconnected the pump and manifold. opened manifold to atmosphere and gauge returns to zero. I hook the manifold back to the schreader valve and it shows vac on the guage. So I have been evacuting the system. To what degree I can't say - the manifold is new to me for 410 and I wonder if the gauge is innaccurate. I have a little 2.5cfm pump, I let it go for 2+ hours. released the charge and all seems well with correct operation. time will tell I guess. thanks for all the helpful replies