Condenser Fan: Description and Operation

[1][2]AUXILIARY FAN - TYPICAL WIRING DIAGRAM

Auxiliary Fan - Typical Wiring Diagram:

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 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 half 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.