The correct answer is C) liquid refrigerant flooding back from the cooling coil. If a refrigeration compressor has a slightly high suction pressure accompanied by an abnormally low suction temperature, it can indicate that liquid refrigerant is flooding back from the cooling coil. This can happen when the refrigerant charge is too high or the cooling load is too low, causing the refrigerant to not fully evaporate in the coil before reaching the compressor. The other options are incorrect because: A) a clogged sub cooler would cause high condensing pressure and temperature, not low suction temperature; B) a leaking king valve would cause low suction pressure, not high; and D) a minor air or non-condensable gas accumulation would cause high suction and discharge pressures, not the specific symptoms described.