Type AST Temperature switch has been specifically designed for use on Diesel Locomotives to safeguard the engine from damage that could be caused by excessive heat. However these switches can be used for other applications also. These switches are of direct mounting design.
 
The thermal sensing element of AST temperature switch consists of a metallic bellows and sensing bulb. This thermal element is filled with a partial vapour charge , the pressure of which rises with the increase in temperature at the bulb. When the temperature exceeds the preset value , the pressure in the thermal system increases and overcomes an opposing spring force to actuate an electrical microswitch. The entire assembly is housed in a uniquely designed die cast aluminium enclosure which allows ease of installation and wiring .