Therefore, a temperature-dependent switch is built into the radiator. If he «feels», that the coolant flowing past it is still too hot after passing through the radiator, the fan is switched on by means of a relay in slot 2 in «eight-pin relay base». It also turns off the fan motor when the temperature at the bottom of the heatsink drops to a certain value.
Two stage motorized radiator fan
Some versions of the Audi A4 have an electrically driven two-stage radiator fan which, thanks to the two-stage switching, can respond more individually to rising coolant temperatures. This is possible thanks to a two-stage thermal switch that enables a second current path to the fan through another relay in slot 3 in «eight-pin relay base» and added resistance.
Radiator thermal switch switching temperatures
Fan model
|
Switch-on temperature
|
Shutdown temperature
|
single stage |
92–97°C
|
About 84°C
|
two stage | ||
1st step |
92–97°C
|
84°С
|
2nd step |
99–105°C
|
91°C
|
Tip: Due to the electrical connection via terminal 30, the fan may suddenly start even when the engine is not running. Be careful when working in the engine compartment!
Thermal switch (arrow) The motorized radiator fan is screwed to the bottom left of the radiator in vehicles with enhanced cooling.
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