Condenser HVAC: Description and Operation

CONDENSER







The compressor pumps the refrigerant to the top of the condenser. Almost all of it is a high-pressure vapor, at this point. Because of its high pressure, the temperature at which it can condense is much higher. The high pressure allows the refrigerant to change from a vapor to a liquid, when ambient air, passing over the condenser, carries some of its heat away. Most of the refrigerant is a high-pressure liquid by the time it reaches the bottom of the condenser. The condenser (like the radiator and the heater core) is also a "heat exchanger."

The condenser on BMW A/C Systems is equipped with an [1][2]auxiliary fan that provides additional air flow through the radiator and condenser, when needed.

[1][2]Auxiliary fan control systems vary from vehicle to vehicle. The following is a typical "basic" example of how an auxiliary fan is controlled.

The [1][2]auxiliary fan is controlled by two normally open relays, a normal-speed relay, which runs the fan at the "normal" speed; and a high-speed relay, which runs the fan at the "high" speed.

The A/C control module grounds the normal-speed relay whenever the A/C system is turned on. This causes the fan to run at the normal speed.

The relays are also energized by a (normally open) double temperature switch, which senses coolant temperature in the radiator. When coolant temperature rises above 180°F (82°C), the normal-speed half of the switch closes, powering the normal-speed relay, and the [1][2]auxiliary fan runs at the normal speed, whether or not the snowflake button is depressed.

When the temperature rises above 190°F (88°C), the high-speed halt of the switch closes, powering the high-speed relay, and the [1][2]auxiliary fan runs at high speed.

There is also an intermediate pressure switch fitted to the receiver/dryer. This switch, which is normally open, closes when refrigerant pressure exceeds 260 psi. This energizes the high-speed relay and runs the [1][2]auxiliary fan at high speed.

The details of [1][2]auxiliary fan controls on other BMW vehicles are different. Refer to the Electrical Troubleshooting Manuals (ETMs) for vehicle specific information.