Car Driveability Controls

By 7 March 2015

An air conditioning compressor takes a significant amount of power to run (on average, somewhere between 10 and 15 horsepower), and the effect of compressor operation, in conjunction with other demands placed on the engine, can impose loads which reduce vehicle performance. This is a significant problem on vehicles with small capacity engines.

Driveability controls are used to control the operation of the compressor to relieve the load on the engine under conditions when driveabllity may suffer. These controls don’t usually affect the cooling performance of the air conditioning system. On most modern vehicles equipped with engine management systems, the compressor clutch is controlled by the electronic control unit (ECU) or the powertrain control module (PCM). The compressor is controlled in accordance with the information received from the various engine management system sensors, to ensure that the driveability of the vehicle doesn’t suffer. This reduces the need for separate driveability controls.

Typical driveability controls include the:
Time delay relay
Wide-open throttle switch
Closed throttle switch
Low vacuum switch
Power steering pressure switch
Power brake switch
Engine coolant high temperature switch
Constant run relay
Compressor delay timer
Anti-dieseling relay
High-pressure relief valve