Refrigerant

An air conditioning system uses refrigerant to absorb heat from the air that passes through the evaporator. Refrigerants are special materials that are vapors at room temperature and liquids at much lower temperatures. Automotive refrigerants, for example, boil at -16 °F to -22 °F (-27 °C to -30 °C). Refrigerants are also able to contain and transport a large amount of heat, efficiently; and they can be evaporated and condensed over and over without being damaged.

In the air conditioning system, liquid refrigerant under high pressure flows through a small hole into the evaporator, where the pressure is then greatly reduced. When the pressure drops, the refrigerant boils and changes from a liquid to a vapor. As it changes its state, it absorbs a large amount of heat.

This is similar to what would happen if a person unscrewed the pressure cap on the radiator, with the engine at operating temperature (Of course, no one should ever attempt this - anyone who tried would be badly burned) The coolant would immediately flash to steam and, in the process, would greatly reduce the temperature of the engine.

As the air passing through the evaporator gives up some of its heat, it becomes colder; it can then be blown into the passenger compartment, to cool it.







Once the refrigerant has absorbed heat from the air, the A/C system removes the excess heat from the refrigerant, and the refrigerant is returned to the compressor.

These are two types of refrigerant used in BMW vehicles; these will be discussed later in the Manual.