Condenser Operation: Refrigerant Sub-cooling

After the refrigerant gas is compressed, it flows -- along with the entrained lubricant -- from the Compressor through the discharge line and into the Condenser (Condensers and Evaporators are also known as "coils"). As the electric condenser fan (or vehicle motion) causes ambient air to flow through the cooling fins of the Condenser, this flowing air absorbs heat contained in the refrigerant that is flowing through the internal Condenser surfaces. Note again that this condensation process takes place at the condensation temperature ("boiling point") consistent with the pressure in the Condenser. The actual condenser pressure (and therefore, temperature) is determined by a number of factors including the rate of air flow across the condenser, its design and physical size, the ambient air temperature and the refrigerant flow rate (compressor size and speed).

When enough heat has been absorbed by the outside air (or, conversely, rejected by the refrigerant), all of the refrigerant gas will become condensed from gas to liquid form at constant temperature. Any further heat rejected to the outside air results in the liquid refrigerant becoming cooler than the boiling point and is known as liquid "subcooling." Generally, the more subcooling, the better because more heat is transferred to the surroundings, and, therefore, more heat can be transferred from the region being air conditioned. (However, subcooling is expensive in terms of condenser size and cost because additional heat transfer area is required to transfer additional heat at a continuously decreasing temperature difference.)