The function of an oil reservoir, commonly known as an oil trap, is to prevent large oil slugs from forming. This is accomplished by trapping a small amount of oil in the reservoir or trap and gradually returning it to the compressor.
The compressor’s discharge line temperature is important because it is an indication of the amount of heat absorbed in the evaporator and suction line and any heat of compression generated by the compression process.
When refrigeration systems are exposed to low-ambient conditions, the condensing pressure (head pressure) will fall. If the head pressure gets too low, the metering device will not have enough pressure drop across it to operate properly.