Icing detection works without a sensor - but how?

[Juschi]

I have here a mobile air conditioner with a single exhaust hose. TROTEC PAC 3500 E. Operating instructions here.

The unit has the function that if the evaporator gets too cold, an anti-freeze function turns off the compressor for a few minutes and reduces the cold fan speed for 30 seconds. So the unit can somehow detect how cold the evaporator coil is and de-ice the evaporator coil.


However, there does not seem to be a corresponding sensor installed. Only two sensors are mentioned in the circuit diagram, and these seem to be the room temperature sensor and the exhaust air sensor:

Circuit Diagram:
CircuitDiagram.jpg

What is called "coil sensor" in the wiring diagram seems to refer to the condenser temperature, see possible error code of the sensor:
Error_Messages.jpg

In the parts list and in the exploded view I only find the room temperature sensor:
Explosm.jpg
PartsList.jpg

The room temperature sensor is a simple NTC, I have found that its temperature does not seem to have any influence on the defrost function.

Can anyone tell me how the defrost function of the unit is triggered if not by a sensor at or on or near the evaporator coil? The De-icing seems to work well that it only becomes active when the cooled air has been around freezing point for a 5 minutes or so.

Thanks!