So you have amicron change over hours of vacuum. temp differences account for that. The big problem is vacuum is vacuum, and if you have a leak you have a leak. Of course if you have a leak pressures will usually go to zero unless it's a pressure leak that only shows under high test pressures. In 20 years I've had only onr documented. It was in a factory weld and only bubbled above 200 psi nitrogen, and then only slowly. The absolute is these are sealed systems and if you pull a long enough vacuum there should be no movement.

 

Not that this is what you are dealing with, but it may help. I just spent 3 days on a large city-multi system trying to find a leak. Turned out to be the head on the expansion valve was leaking around the threads. Only found it by separating the individual parts of the system, isolating and pressurizing as i went. Hope this helps, also Mitsubishi okay's pressure testing up to 200psi on the completed system and wants 600 psi on their line sets (but the valves on the condensing unit are only rated for 250 so go figure). Good Luck

 

Did you use a preflared lineset? I had a leak on one flare on mine when I put it in in october. Made new flare and all is good.

 

I'm not sure about the model of mitsubishi you are dealing with, but the ones I've installed don't have a factory nitrogen charge. I would second guess your installer. Its not that difficult for an installer or technician to diagnose if there is a leak before the system is started.

 

Mitsubishi requires a much higher pressure check,something along the line of 500 psi they also require you to use a torque wrench to tighten the flare fitting.and I seem to remember that the flares require percentage or pitch like 45 degree angle or something like that .and no brazing or soldering of the line sets at all or the warranty is no good

 

Thanks, I wonder why they void warrant for brazing.

 

Hey if you want a cool web site for Mitsubishi go to www.mylinkdrive.com. It's a great web site for trouble shooting their product, you can also download for free their service and trouble shooting guide

 

sometimes micro leaks barely bubble when you put leak detector on joints. Not sure what brand of bubbles you use but BIG BLU is the best. If there is a micro leak you will see foam, not bubbles, kinda like spit. IMO try more than 100 psi. of nitrogen or add some 410-a and get out your electronic leak detector.

 

They don't want you to braze, because there is no LLFD, and it's got a tiny metering device.

 

OP: You've got a leak. Somewhere. The units don't come nitro precharged.

 

Check your gauges. Especially if you have low loss fittings built in to your hoses. I had same problem and after ripping my insulation apart trying to find a phantom leak I pressurized to 300 psi and left overnight with no gauges. Found all 3 hoses leaking on the crimped end of my low loss fittings on my hoses.

 

Where does it say That brazing will void the warranty

 

I agree that they don't "void warranty".
Just that the manufacturer does not recommend brazing.

In reality, one of the reasons fujitsu and mitsubishi units are flared instead of brazed, is based on the located they were designed.

In japan, construction is and has been completely different. Closer housing, using more combustible surfaces. Using a torch, is considered very dangerous. Fire in japan spreads rapidily, due to this combustible material and close housing.

Or so I've been told.

 

The Mitsu rep in the Virgin Islands told me brazing was fine IF I used a nitrogen purge to prevent carbon. Then he would warranty it. And no, the evaps are not pressurized at shipping.

But I never had any issues. All of the Mitsubishi Mr. Slims I installed were 100% bulletproof. The only failure I ever saw was where a family of lizards crawled between the board and backplate on a P-Series and shorted out the board. Even after the salt air dissolved the condensers to the point where the fins were dust barely holding on, the stupid things still ran fairly decent. Amazing piece of machinery. :yes:

 

I have brazed fittings on minis many times. They like to keep it to a minimum due to all the strainers and cap tubes and LEVs.

Be sure to flow nitro and you will be fine. They don't void the warranty just because you have to braze something.

Google "Lokring" for a press type fitting available for refrigerant piping. We are currently using it on a City Multi job and its fast and easy with no contamination.