IF you know how to do it, get these!
https://www.ebay.com/itm/4-Valve-AC...m=261977731046&_trksid=p2045573.c100505.m3226
You can buy a canister of R134a for under $150 for 30 pounds and you DONT need to be certified to get it.
I have a better set than them, and they come with R22 connections, 410 connections and the ones for automobiles for R134a. You can monitor both sides then. Its VERY important to see both high and low side. The compressor appears to turn, even if it isnt. Notice how the pully turns, but the clutch assembly isnt when not engaged, but yet when engaged spins with the pully. They do cycle on and off, ALL systems do! If the system is low on refrigerant(please dont call it freon cause it isnt), the lines will sweat some but it wont cool much when the outside air temp is above around 70 degrees and humidity is over 50%.
If the compressor is running, and the low side says 100PSI, it is WAY OVERCHARGED, which then wont cool either... You have to get some refrigerant out, but you arent legally suppose to let it out in the air, your suppose to recover the refrigerant.