Expansion valve is a part that serves to control the amount of coolant that enters the evaporator. When speaking about its construction, the expansion valve is a variable section throttle. This spare part is set up behind the drier’s filter on the evaporator inlet branch. Its main function is to reduce coolant pressure and temperature to such a limit that when passing through the evaporator evaporation and intensive heat exchange to be provided. As for the sensing hole, it lowers the pressure of the fluid entering the valve. That coolant that enters the drier filter is a liquid under high pressure.

When the coolant passes through expansion valve opening, it is sprayed. At the same time, the temperature and pressure of the substance decreases. This is necessary to facilitate the entire evaporation process of the coolant directly in the evaporator. To find out how the amount of the coolant that passes through the thermostatic expansion valve is regulated let us describe the process. In thermal contact with the evaporator exhaust pipe there is located temperature sensor.

Inside it in the capillary tube and the bellows there is gas - coolant. When the temperature of the exhaust pipe is increased, the pressure of the coolant in the sensor respectively increases and the bellows stretches. Through the traction bottom of the bellows pressures on the ball or needle that increases coolant flow when moving. It passes through the expansion valve and causes temperature decrease of the output tubes and evaporator. As a reaction, coolant pressure in the sensor is reduced, the bellows is compressed and the ball closes the throttle. This results in coolant flow reduction.

If it was diagnosed that the expansion valve is damage, it must be replaced by a new one, since it is not subject to repair.