I have a 3 ton unit. Suction pressure is about 75 and condenser temperature is 120 (outside temp 90 degrees plus condenser factor for a fan cooled unit 30 equals my 120 degrees) T-stat is set for 80 degrees and room is also 80 degrees and the air coming out of the vents is about 64 degrees. Is my unit charged properly? It seems to never satisfy, but remember day time temp. here in Florida is about 95 degrees. Next question should I charge unit by suction pressure or discharge temp. I know as a rule of thumb suction pressure should be between 60-70, but if I charge the unit this way won't my head pressure also fall even know the pressure is 5 psi out of range. This unit is R-22

Charge your unit by superheat or subcooling depending upon what type of metering device is being used. Use Google for the above terms.