Regulating The Air Conditioning (A/C) Compressor

Courtesy of VOLVO CARS CORPORATION

The air conditioning (A/C) compressor is controlled by the Engine Control Module (ECM) (4/46) on request from the Climate Control Module (CCM) (4/6) via the Controller Area Network (CAN)). When the Engine Control Module (ECM) receives a signal from the Climate Control Module (CCM) to activate the air conditioning (A/C) compressor, the Engine Control Module (ECM) grounds the circuit for the relay coil for the A/C compressor. See also: DESIGN  

The relay (2/22) closes the circuit between the integrated relay/fusebox in the engine compartment and the clutch for the air conditioning (A/C) compressor (8/3). The air conditioning (A/C) compressor which has a variable cylinder displacement is always running during normal driving. Displacement in the compressor is regulated by a solenoid which is controlled by the Engine Control Module (ECM).

The Engine Control Module (ECM) controls the solenoid (displacement) from the driver's and vehicle's various driving characteristics. At engine start, driving off and at acceleration etc, displacement is controlled so that the AC compressor has the least possible effect on the engine torque. The Climate Control Module (CCM) controls all functions in the climate control system that are related to the vehicle's interface for driver and passenger, i.e., the climate control system buttons on the dashboard environment panel. Also see appropriate Design and Function information for the Climate Control Module (CCM).

The Climate Control Module (CCM) transmits information to the Engine Control Module (ECM), which determines what must be prioritized. For example, the air conditioning (A/C) compressor in certain extreme cases is switched off completely, regardless of the Climate Control Module (CCM) request. This is to prevent negative engine performance and to protect the air conditioning (A/C) system. As well as the information from the Climate Control Module (CCM), the Engine Control Module (ECM) controls the air conditioning (A/C) compressor based on the information from:

• Air conditioning (A/C) pressure sensor (high pressure side) (7/8)
• the throttle position (TP) sensor (6/120)
• the engine coolant temperature (ECT) sensor (7/16).