Spring quiz. What is it?

[dephead2004]

So nearly 3 years on from first ownership, I got to wondering what the small black circle is in the centre of the fan controller. It's not a switch so what is it?

A few experiments later confirmed it's the............

Answer to follow in a few days unless you all know already and it's me just being Captain Slow.

 

[kiddo]

Temp sensor?

 

[dephead2004]

Temp sensor?

Yes it's part of the temperature control system on climate control heating systems



It's a thermistor which controls the temperature of the air coming from the vents.

Here's the experiment.

With the car warmed up put your finger on the little black disc and leave it there for a few seconds. As the sensor thinks that it's getting hot in the car because your finger is around 37 degrees C and the car thermostat is set lower than that maybe 20 (unless you like a hothouse), the thermostat tells the hot water valves to close. The air gets cooler over about a minute

Take your finger off the disc and the air temperature from the vents increases.

Extra homework: does the fan speed increase or decrease as you do this?