Coolant Temperature Sensor / Switch HVAC: Description and Operation

Function
The ECT sensor sends a resistance value corresponding to the coolant temperature via the instrument cluster and the serial interference (K1) to the pushbutton control module.

Here the value is processed and the A/C compressor is switched off in two stages as follows:

Stage 1
At a coolant temperature > 123 °C the duty factor is reduced by 50%. In this case the A/C compressor is switched on in cycles, i.e. off approx. 20 sec. and on approx. 20 sec.

If the coolant temperature drops to below 123 °C the A/C compressor is switched on again permanently.

Stage 2
At a coolant temperature > 127 °C the A/C compressor is switched off completely.

When the coolant temperature drops to below 127 °C the A/C compressor is switched back on in the cycled mode (stage 1).