Whats this plug for?

[Hyperion]

Hi

I was having a look at my cars engine, and noticed that there is a brass looking plug on the drivers side of the radiator with three wires plugged in. The plastic plug is very brittle.

My car is a 1990 325i Automatic with Aircon.

Questions:
1: what is this for?

2: does BMW still sell the plastic plugs they use everywhere in the engine bay, (fog lights, main beams, this plug, etc.)

Pic:


Uploaded with ImageShack.us

[daimlerman]

That gadget switches the electric fan on and off,as required.
Replacement plugs should be available.

[Hyperion]

thanks,but, electric fan for what.....
I had a quick look and i see only 2 fans, the one above ( in the pic) turns as soon as i switch on the car, and the other fan i can see is in the front of the car , which switchs on when i put on the aircon.

[daimlerman]

Aircon fan!

[Hyperion]

sorry dont want to be a dumbass, but i dont see the link between the plug and the aircon fan, how does it work?

[daimlerman]

I use a plug fitted in the same place to switch an electric fan on my M50 conversion,it gives me an automatic two speed electric fan,switched by a thermostat located within the plug.
I assume that the air-con fitment that you have works in the same way.

[Brianmoooore]

The fan in your first pic. is driven by the engine, via the fan belt, and a viscous coupling. This viscous coupling normally allows the fan to just freewheel - the forward motion of the car is normally enough to cool the radiator. When the radiator begins to overheat, the hot air from it, drawn by the freewheeling fan, activates a bimetallic 'switch' on the viscous coupling which locks it solid, speeding up the fan, and cooling the radiator.
When the aircon is used when the car is stationary, there is insufficient airflow to cool the condenser (radiator) of the aircon system, so the electric fan in front of your radiators is switched on at low speed. The electric fan is also arranged to switch on at low speed without the aircon being on if the radiator begins to overheat. This is done by a thermostat on the side of the radiator - your 'brass plug'.
There is also a second thermostat in the brass plug, set at a higher temperature than the first (hence the three wires), which switches the electric fan to full speed, shifting a serious amount of air, if the radiator reaches a high enough temperature.
The plastic outer shells of the plugs should be available from BMW, but identifying the exact ones you need can be fun.