Table 2 shows a refrigeration system with a dirty condenser causing restricted airflow over the condenser. A similar condition would be a defective condenser fan motor starving the condenser of air. Both conditions caused the head pressure and thus condensing temperature to increase. Even the liquid at the condenser’s bottom will be hotter because of the elevated condensing temperatures. This creates a greater temperature difference between the liquid at the condenser’s bottom and the ambient (surrounding air) designed to cool the condenser and its liquid. This will cause the liquid at the condenser’s bottom to lose heat faster, causing more condenser subcooling. In this example, high condenser subcooling is not caused from an “amount” of liquid being backed up in the condenser, but from the liquid in the condenser’s bottom simply losing heat faster.
This phenomenon happens because the temperature difference between the liquid at the condenser’s bottom and the surrounding ambient is the driving potential for heat transfer to take place. As more and more air is restricted from flowing through the condenser, the amount of condenser subcooling will increase.
Notice that the system check sheet shows higher than normal condenser subcooling of 15?. This system check sheet looks very similar to an overcharge of refrigerant because of the increased subcooling amounts, but do not be fooled by it. When a high head pressure and high condenser subcooling is experienced in a refrigeration system, the service technician must not assume an overcharge of refrigerant. The technician must first check to see if the condenser is dirty or a condenser fan is inoperative because of similarities of symptoms in both scenarios of an overcharge of refrigerant and restricted airflow over the condenser.