Yeah you need both high side and low.side pressures to determine if its charged properly. A rule of thumb is in warmer weather your high side should be 2.5 times ambient temp. So if its 80 outside then your high side should be around 200psi. If its 140 on high and low side is showing 35 it would be under charged. Single guage recharge kits are a gimmic and your guessing at when its full.
