Micron rise with respect to valve core removal tool

russen99

Vacuumed out my mini split system with a core removal tool and micron gauge. Got a decent vacuum but when I went to reinstall the valve, it jumped to 5000 microns and slowly increased. My first theory was that after isolating the system with ball valve and disconnecting the vacuum hose to reattach the plunger in order to reinstall the schrader valve, a small amount of air is effectively introduced into the system. However, is it enough to cause such a spike?

Here is my process in case I did something wrong:
-Installed core removal tool (CRT) with attached micron gauge directly to service port.
-Removed schrader valve, but not the plunger assembly, and closed the ball valve on the CRT.
-Removed plunger assembly
-Attached vacuum line to CRT, turned vacuum pump on then opened CRT ball valve
-Vacuumed down until steady at 130 microns
-Closed ball valve on CRT to isolate system and turned off vacuum pump
-Observed rise in vacuum until stabilized around 270
-Removed vacuum pump hose and reconnected plunger with schrader valve
-Opened CRT ball valve and watched micron gauge rapidly climb to 5000+ microns and slowly continue to climb thereafter. I would expect some rise due to the volume of air introduced between the plunger assembly and the CRT ball valve. To what extent I am unsure, but 5000 microns sure seems unacceptable and negates the vacuuming process.

Repeated this again and watched the same thing happen. To me this indicates there is a leak in the plunger seals. This was a brand new Yellow Jacket CRT.

GW

For some reason I can't follow your steps. When you shut the ball valve, you should be taking the pump, hoses, all that stuff off of the vac gg.

Only the line sets, CR tool and vac gg should be left. If this how you did it? One side of the ball vale is a deep vac, the other side of the ball valve is whatever.

When we do this and are happy with the holding vac we open the service valve and allow some refrig to pressurize the system. THEN we put the schrader core back in. Then we fully open the service valve and dump all the refer into the line sets.

ChrisJ

You should have charged the system before reinstalling the core.
Never mess with that when the system is below atmosphere.

They all leak some around the plunger, but it doesn't matter because the system should be pressurized when you're using it.

After pulling your vacuum isolate the system from your pump and wait to see how much it climbs. If all is well, release the charge. Once the system is pressurized go ahead and remove your hose and reinstall the core.


Also, if you struggle trying to get the core in, try loosening the core removal tool a hair on the charge valve as you're wiggling the plunger around. If done right, it'll slide right back in and no gas, or, very very little should be lost.

ratio

As @ChrisJ said above, you can't put the core back when the system is under vacuum. Even that little bit of air in the core tool is enough to break the vacuum. That can only be done at atmospheric or positive pressure. As I often have to remind my guys, you can't leave a system under vacuum. Even taking the hoses off is enough to break a vacuum.

Protip: if you have to add juice due to lineset length, add it before you open the valves on the condenser. You'll fit a lot more of the added charge into the system, maybe all of it.

JUGHNE

In my method of madness for any new install of linesets I do:
Remove the cores before any connection, brazing etc.
Screw the hoses directly onto the port.
Bleed N2 for brazing.
Flush any air out of everything with N2.
Pressurize to 300-500 for leak testing.
Dump N2 charge and start vac pump before it is open to air.
Vac first time, watch micron with pump off.
Pressurize with N2 for first cleansing.
Dump N2 charge and start vac pump as above.
Vac 2nd time, observing micron again with pump off.
Pressurize with N2 again.
While system has 10 PSI or so I re install cores with positive N2 pressure coming out of fitting. Can bleed N2 in opposite side while installing core....do same for other side.....keeping system always under positive N2 pressure.
Then vac 3rd time with cores in .......check micron hold level.
Crack liquid line valve to pressurize system with refrigerant.
Close liquid line and install quick connects on both hoses. Reopen liquid valve and then suction valve. Done.

I don't ever use quick connects on vacuum, only with pressure will they seal very well.
With this method I don't need or want to use core removal tools for this process. Less threaded connections.
Just don't forget to install the cores for the 3rd vac.

ratio

A triple evac it's the way to go if you want a clean, dry system. Pretty sure it's even faster than trying to do it in a single shot.

I don't remember if I told my triple evac story here before, but one time my 'tard left the lineset to a mini split open, pointing straight up on the roof. The first pass with N₂blew water out of the pipe. An hour later it held at under 500 microns. Now, the lineset was only about 20-30', but it made a believer it off me nonetheless.

ChrisJ

My 100 micron pull was a single pull but for many hours.

JUGHNE

IIRC, the logic of the triple evac was that the first one removed 95% of air, non condensable gases and moisture.
After purging with N2 this left 5% of nasty's in the systems.
The second evac removed 95% of the remaining 5%.
The third one removed 95% of the next remaining 5%.

I may not be right on the numbers but that was the theory.
We just hope that dry N2 is really that....dry.

ratio

My experience seems to indicate that it is dry, very dry. A few 5 minute evacs with N₂ will get you further than a single hour-long one without. Purging has a similar effect.

I don't know the truth of it, but I've heard that industrial dry gases are dryer than medical dry gases. Kind of makes sense, our biology is a lot more tolerant of water than many of the processes we use gases in.

ChrisJ

ratio said:

My experience seems to indicate that it is dry, very dry. A few 5 minute evacs with N₂ will get you further than a single hour-long one without. Purging has a similar effect.

I don't know the truth of it, but I've heard that industrial dry gases are dryer than medical dry gases. Kind of makes sense, our biology is a lot more tolerant of water than many of the processes we use gases in.

the climb after shutting down the pump indicates how dry the system is.

For example, mine climbed to 120 microns and stabilized with no increase even after 20 minutes. That was a very, very, dry system.

Triple evacs speed up the process, especially on a system that may be on the wetter side. But the moisture will get to the pump eventually, given enough time.

ratio

Right. I always meant that a triple evac sped up the process enough that it's a significant win, time wise. At least, with the stuff I deal with. IDK much about appliance-sized systems. 4-150 lbs of refrigerant is the size I mainly deal with. A triple evac, along with a ½" vacuum hose & a four port manifold, sucked down that 147 lb system to below 500 microns in just a few hours on the final pull. That's with one 7 CFM pump.

ChrisJ

ratio said:

Right. I always meant that a triple evac sped up the process enough that it's a significant win, time wise. At least, with the stuff I deal with. IDK much about appliance-sized systems. 4-150 lbs of refrigerant is the size I mainly deal with. A triple evac, along with a ½" vacuum hose & a four port manifold, sucked down that 147 lb system to below 500 microns in just a few hours on the final pull. That's with one 7 CFM pump.

My 100 micron pull was on my 3 ton system, approx 7 pounds of 410A. I'm not positive, but I want to say that was a 6 or 7 hour vacuum. I had time.

Oddly enough, the antiques I work on, also sometimes take a decent amount of time to pull down, I think because of the old oil, and maybe some methyl formate staying behind etc.

JUGHNE

Yes, just as there is a big difference in just doing a new line set/coil verses a complete system including the cond unit. Gases trapped in oil in compressor and tubing.

HVACNUT

Might not be the core remover tool at all. Could be a bad flare or braze.

ChrisJ

HVACNUT said:

Might not be the core remover tool at all. Could be a bad flare or braze.

It did it when he went to install the core, which is very easy to believe as you should never do that. Core removal tools are far from tight.

GW

the core removal tool is simply an exercise in reducing the amount of fittings on the vac process

ChrisJ

GW said:

the core removal tool is simply an exercise in reducing the amount of fittings on the vac process

Sure, without the "core removal" part until pressurized.