Probable Cause:
Load too high, has there been a recent addition to the design load
Low refrigerant charge
Low refrigerant flow due to liquid line restrictions.
Faulty control circuit, may be low pressure controls or capacity control.
Evaporator coil iced or dirty.
Refrigerated or air-conditioned space has excessive load or poor insulation.
Dirty condenser.
Blocked filters.
Hot gas bypass or false load valve stuck.
Compressor valve leaking
Undersized TEV.
Faulty EPR or pressure setting too high.
Remedy:
Choose a condensing unit with increased capacity to match load requirement.
Fix leak and charge.
Check and repair liquid feed problem.
Determine fault and correct.
Check and repair defrost system, clean evaporator and/or drains.
Determine fault and correct.
Clean condenser.
Clean or replace filters.
Check, repair or replace.
Check high and low side pressures (leaky valve will not be able to develop proper suction or discharge pressures).
Replace EPR or adjust pressure setting where needed.