Blower Control

Blower Control

In the automatic mode, blower speed is determined from reference temperature maps. In general terms, the more heating or cooling required to achieve the temperature selected on the control panel with the driver's side temperature switch, the faster the blower speed.

When maximum cooling is first required in the automatic mode, the ATC (automatic temperature control) module runs the blower at full speed for a fixed period regardless of any drop in passenger compartment temperature. Different time periods are incorporated for the following markets:
^ NAS and Gulf States
^ Europe and ROW
^ Japan.

NAS and Gulf States have the longest time period with the blower at full speed and Japan the shortest. T4 can be used to change the market setting so, in some cases, if a customer complains of the duration the blower runs at full speed, changing the market setting could resolve the complaint.

When heating is required, blower speed is reduced if the engine is cold and then progressively increased to the nominal setting as the engine coolant temperature increases from 20 to 50 degrees C (68 to 122 degrees F).

On the automatic system, blower speed is also influenced by the sunlight sensor. At high light levels blower speed will increase to increase the cooling effect.

When the blower is selected off temperature regulation is no longer possible so the ATC (automatic temperature control) module disengages the A/C (air conditioning) compressor, de-energizes the auxiliary water pump and closes the coolant valves. Pressing any of the A/C (air conditioning) system switches restores blower operation and activates the required function. If the blower is selected off when the ignition is switched off, the blower remains off if the ignition is switched on again within 15 minutes. If more than 15 minutes elapses between the ignition being switched off and back on again, the ATC (automatic temperature control) module switches the blower on at speed 1.

If battery voltage is low the ATC (automatic temperature control) module reduces blower speed to conserve power. If battery voltage decreases to less than 12 V, the ATC (automatic temperature control) module decreases the blower signal voltage, and thus the voltage to the blower motor, in direct proportion to the reduction in battery voltage.