Termobimetallicheskih sensor TM used as a relay for electric fan in the cooling system of the engine, very often fails. In hot weather, in heavy city traffic the fan runs almost constantly. As a result burn the contacts of the sensor on the fan, and you cannot restore them.
After repeated substitutions of this sensor, I made an electronic relay, where the sensor is used "regular" thermoresistive temperature sensor TM, which is controlled by the engine temperature.
The layout of this temperature switch works flawlessly for many years. The primary node in it is a Schmitt trigger, collected on transistors VT1, VT2. The trigger input is connected to the thermoresistive sensor R1 TM. Resistor R2 is the threshold of the relay when the temperature of the liquid...94 92°C. With the collector of the transistor VT2 control signal is supplied to the electronic key on the transistor VT3, which in turn includes actuating relay K1 fan motor M1 engine cooling. The Zener diode VD1 prevents false tripping when the fluctuations of the on-Board voltage of 12 V.
The circuit Board is installed in the housing of any old relay type PC-527, and the transistor VT3 set screw on the housing for better cooling.
Author: P. Bialiatski, Novosibirsk region, Berdsk; Publication: N. Bolshakov, rf.atnn.ru