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I'm installing a new Daikin 4MXL (36K BTU) outdoor compressor, with 24K and 9K indoor unit (I previously installed a smaller dual zone Daikin)

One of new indoor unit's lineset will be behind drywall, so I cut off flare joints and to solder on sleeves. So I need to nitrogen purge. I have a nitrogen tank and a purge valve on the regulator to get the flow 2-4 PSI when I'm ready.

But I can't get it to work in concept with higher pressure (around 100 PSI). Something doesn't seem to be flowing right.

Both indoor units are connected to the outdoor compressor with flares that wrench tightened but not too tight (e.g. not torqued down yet).

Same for flares on 24K indoor unit. The 9K indoor air handler's lineset is the I have sleeves on to join pipes with flux paste in them. They're ready to solder.

So it is now a complete closed lineset circuit between the indoor and outdoor units.

Here's the problem - I can't verify that nitrogen flows all the way through properly in order to start soldering.

INJECTING NITROGEN INTO LIQUID SERVICE PORT "blocked": I tried about 100 PSI of nitrogen into liquid side service port. Seems to almost immediately get stopped in some short run of pipe by sound of it. I turn off the gas, unscrew the adapter and it and injected out quickly and briefly:

INJECTING NITROGEN INTO VACCUM SIDE SERVICE PORT "DISAPPEARS": When I try flowing 100 PSI into vacuum side service port, I hear the gas flowing into the pipes, pressure keeps dropping in my nitrogen cylinder, I keep hearing gas go into the pipes (when doing it for a minute or two). Soap test on flared connections at unit don't bubble, yet I don't feel anything coming out the liquid side service port with a wet finger. Seems like 100 PSI would be more than enough to let some gas all the way through and enough to feel if I'm putting 100 PSI in, even if some flares are leaking slightly. It's likeleaking somewhere inside or getting misdirected. (note, new unit and I never powered up or toughed allen wrench valves to release refrigerant)

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OK, the problem was that I let too much nitrogen in the service ports initially and blew apart a connection I was going to solder (sleeved copper tubes) inside the house and it was leaking refrigerant. I thought maybe it was pipes filling up or a leak inside the outdoor compressor or something.

(I lost too many PSI to do the 550 PSI pressure test by over-reacting and experimenting so now have to haul the tank in for a refill)

After closing all the loops (soldering) I discovered I still can't flow nitrogen from one service port (low side) to the other (hi side) or vice versa. I suspect a valve in the outdoor unit stopping it but don't know enough of the internals to figure it out.

But I think what I can do is disconnect the high side line of the indoor unit I want to nitrogen purge, and then the low side service port will feed the low side line of that indoor unit loop and probably exit the disconnected hi-side line at the compressor so I can have gas flowing when I solder. Will test that today.

Other things I learned is, better to use hard solder not ordinary silver solder, but brazing is better because if there's a fire in the house the joint is unlikely to melt and leak R410A into the fire (someone said that makes it toxic, not sure).

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