Air Conditioning (A/C) Relay

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2009 Volvo S60, 2008 Volvo S60, 2007 Volvo S60, 2006 Volvo S60, and 2005 Volvo S60. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Air Conditioning Relay

Courtesy of VOLVO CARS OF NORTH AMERICA.

The air conditioning (A/C) relay supplies the A/C compressor with voltage. The relay is controlled by the engine control module (ECM) based on information from different signals:

the climate control module (CCM) (via the control area network (CAN))
the engine coolant temperature
the position of the accelerator pedal (AP)
the pressure in the system.

The engine control module (ECM) can temporarily disengage the A/C compressor during wide open throttle (WOT) acceleration.

The relay is mechanical. It has a closing / breaking function and is supplied with power from the system relay.

In the rest position the circuit in the relay is open.

The system relay supplies the coil and the relay with power. The relay activates when the coil is grounded in the engine control module (ECM), the circuit closes and the A/C compressor is supplied with power via the relay voltage output.

The relay coil is grounded (signal) when the engine control module (ECM) receives a signal via the Controller area network (CAN) from the climate control module (CCM) to activate the relay and start the compressor.