HVAC pros - help with pressure gauge and mini split install

I am working on installing a mini split. I rand the lines today and made the connections. The flares from the factory looked clean and decent and I used nylog on them. I purchased a digital pressure gauge and two valve stem removal fittings with valves. The pump I bought really sucks and will not take it down below 8900 micron but I could be doing it wrong too. I watched several videos on how. I did not pressure test it with nitrogen.

So the pressure gauge will sit and vary between 8900 and 8750. If I rotate the valve and til the gauge towards the ground the pressure shoots up to 10,000 but then goes back to 8900 when rotated up.I have no idea whats goin on with that

My main question I guess is if there was a leak in the system wouldn't the pressure would go up and stay up and never go further down or vary downward?

I will probably have an HVAC guy I know come vacuum is for me. I was at least try to see if it leaks. Oh, I see them make little gaskets for flare fittings. (flaretite) do these work and are they OK on HVAC stuff.

 

As you suggested, I’d call the HVAC professional that you trust. The system should be pressurized to 500 psi with nitrogen, and leak checked at all joints and flares before starting the evacuation. I don’t know what your evacuation equipment looks like, from your vacuum pump to your hoses and gauge manifold. Not all hoses and core removal tools are vacuum rated. If you can’t get it below about 9000 microns that could just be indicative of the size of your leak, or perhaps the pump has a gas ballast that is open. One way to know if it has a leak is to isolate the pump from the system, with the micron gauge reading the system. If the microns continue to climb and don’t stabilize, there is a leak. As for the flares, all a good flare needs is a drop of vacuum pump oil on the face. I wouldn’t use o-rings or gaskets of any type. They should also be 45 degree flares.

Call the Pros if you want a system that is dry and tight, and will run for a while. HVAC isn’t as DIY as other skilled trades IMO, if not done right the system has a good chance at being nothing but problems in the future.

 

Here is how I isolated the vacuum gauge. The pink valve was shut off and the pump disconnected. and the gauge remains at 8900. The valve core is also removed.

 

It also might help if I took the needle valve out of the red hose. This is why I should stop working on stuff when i get tired.

 

Update: this morning I was able to vac it down to 390 micron and it held and is working fine. I have a friend who is an HVAC tech whom I was able to talk to. He said anything 500 or under is OK for vacuum in AZ and with out elevation.