Description & Operation: Operation: Notes

WARNING: This page is about a different car, the 2006 Land Rover Range Rover. However, it is still accessible from the selected car via links, so may be relevant.

Both the manual and automatic systems operate on the reheat principle. The air entering the heater assembly is cooled to a constant value by the evaporator and then reheated as necessary by the heater core to produce the temperature(s) selected on the control panel.

To determine the various system settings, the ATC module derives a reference value (called the Y factor) from:

The temperature setting on the control panel.
The ambient temperature.
The in-vehicle temperature.

The reference value is measured in %, where -27.5% means maximum cooling is required and 100% means maximum heating is required. On the automatic system, separate reference values are produced for the left-hand (LH) and right-hand (RH) sides of the heater assembly.

On both the manual and automatic systems the reference value is used for temperature control. On the automatic system the driver's side reference value is also used for door positioning and blower speed calculations.

When the ignition is turned off the ATC module memorizes the system settings and resumes the same settings the next time the ignition is switched on.