Vaccum doesn't seem to hold..

[crabjoe]

Ok.. I'm starting another thread because I find this confusing.

I put a vacuum on my newly installed heat pump and I can get it down to 280 microns. I could probably get it down further if I let it run longer, but let me tell you the story....

I have the manifold gauge hooked up and the micron gauge is on the lowside, next to the gauge.

1st time, I run the vacuum pump, my micron gauge shows 350 within about 20 mins.. It might have gotten there quicker, but I walked away.. I shut the manifold gauge valves and the gauge starts climbing. I open them back up and turn the pump back on and it drops super fast and got even lower, below 300 microns... I close the valves and it starts climbing again... Goes to about 1200 microns and it looked to have stopped climbing... I didn't give it more then a couple mins.

I'm at a loss here because it doesn't seem hold vacuum. You would think if it can get down that low, there's no leak, but the gauge climbs.. I just don't get it.. I google the issue and on a HVAC site, the same issue happened to a few other guys but the other pros never gave a clear answer as to why this happens, even though some seem to say it was normal... If this is normal to some, why is that?

Should I try hooking the vacuum up, without the manifold gauge to see what happens? I know that when I pressurize the line set with 250 psi of nitrogen, it doesn't budge for over an hour....

Oh one other thing... I wanted to leave just a bit of pressure in the line, since I don't have power to it yet, so I pressurized the high side. I expected the nitrogen to flow through the TXV and the pressure to equalize, but it didn't look like it was happening.. Is this normal, or did I jack up my TXV when brazing? I had a ton of cool gel on it during the brazing process... and had to wipe off the excess, when I was done...

 

[Jackfre]

If you opened the service valves you have dumped the factory charge and you don't know what is happening. You now have to dump the charge and do the nitrogen pressurization of the system first. Is the line set tight? Is there any leakage in the service valves? You should do a triple evacuation before doing a full re-charge of the factory pre-charge plus the additional refrigerant you added. Step by step!

 

[crabjoe]

I haven't open the service valve.. so unless they're not tight, the factory charge should still be in the compressor.

 

[brewchief]

Normal gauge hoses are not vacuum rated and will leak slightly, if you have pressure in it now soap bubble your fittings to make sure they are good then pull it down as low as you can get it, if you are well below 500 microns you should be good, let it run for a half hour or longer at that point then open the service valves or add refrigerant from a jug if needed.

TXV should be fine as long as you kept the body and sensing bulb fairly cool.

Sent from my XT1254 using Tapatalk

 

[LS6 Tommy]

All of the above and once again,

YOU CANNOT USE VACUUM TO LEAK CHECK.

Tommy

 

[monkeyspanners]

Could be moisture if it tops out at 1200 microns. Put some fresh oil in your vacuum pump and try again. (Change the oil when its hot)

 

[pop pop]

If you've changed the pump. oil and still don't get a good reading, use metal lines instead of your rubber gage set. Those flex lines are porous. If you don't get readings with metal lines, you have a leak or moisture. Find and fix, but leaks are found with N at pressure.