We need superheat temperature or coil temperature, freezing temperature
Normally if you know coil temperature consider delta 3°c
i.e coil temperature 6°c
6-3°c = 3°c
Hence let us consider 3°c and refrigerant R-22
by using p-t chart
3°c = 80 psi
to get suction pressure
Suction pressure = Absolute pressure – Atmospheric pressure
Suction pressure= 80-14.7
Suction pressure= 65.3