Expansion Valve: Description and Operation

Design:

The expansion valve sprays liquid refrigerant into the evaporator.

When the A/C compressor switches on the pressure in the evaporator decreases causing the diaphragm (1) to arch downward. The tappet (3) follows the motion of the diaphragm and presses the valve ball (4) away from its seat against the force of the spring (5). The refrigerant is sprayed into the evaporator through the open valve. Since the motion of the diaphragm depends on the intake pressure as well as the temperature at the evaporator outlet, only the amount of refrigerant is injected that can be evaporated optimally.