Vehicle Speed Sensor: Description and Operation

The Air Conditioning Control Module A/CCM receives a road speed signal from the instrument pack, derived from the Antilock Braking System Traction Control Module ABS/TC CM.

This signal is required to control the blower fan speed to minimize the effects of ram air, i.e. blower fan speed changes in proportion to vehicle road speed.

The signal also determines the frequency at which the ambient air temperature is updated. The road speed compensation for blower control is inhibited when the selected temperature is 'LO' (maximum cooling), 'HI' (maximum heating) or defrost mode and airflow is set to maximum.