Hello, I can help you with this. The low side tap is on the compressor stem, the high side is not accessible unless you tap it (at the filter drier). Based on the fact that you had a frost ball near the compressor, I'm sure you have a leak (low pressure). You should have 10lbs at the compressor. If low then you have a leak if above 20 then you have a weak compressor. I find there is no need to check high side. If you have leak then you will need to replace the evaporator. Let me know what you find and I can assist you further. Thanks, Sam
Also the refer compressor is the one on the right.
after replacing the evap, how can you recharge without attaching to both low and high. i have 25 vehicles and 100 heavy machines and we repair the AC all the time but always charge through the hi side and watch the lo.