CAB AR 2013572 - Caterpillar

Illustration 1 g01507656
(1) External equalizer line (2) Metered restriction (3) Outlet (4) Capillary tube and temperature sensing bulb (5) Diaphragm (6) 90° style expansion valve (7) Inlet (8) Ball and rod (9) SpringThe expansion valve (6) is designed to convert the refrigerant from a high pressure and high temperature liquid into a low pressure and low temperature liquid vapor mixture. The expansion valve also controls the amount of refrigerant that is supplied to the evaporator.The two main types of expansion valve are the 90° expansion valve and the block expansion valve. The internal operation is identical for both of the valves. The valve configuration on the air conditioning system can be found in Systems Operation, "Refrigerant Expansion Valve System" within this manual.The liquid refrigerant with high pressure and high temperature enters the expansion valve at the inlet (7) from the condenser. An amount of refrigerant is allowed to flow through the metered restriction (2) and the outlet (3) to the evaporator.The size of the metered restriction is controlled by three components:
Pressure in the capillary tube (4)
Pressure in the external equalizer line (1)
Force due to the spring (9) The capillary tube is filled with saturated refrigerant. There is a temperature sensing bulb at the end of the capillary tube. The temperature sensing bulb is held to the evaporator outlet. As the temperature of the evaporator outlet increases, the pressure in the capillary tube increases. This pressure creates a downward force on the diaphragm (5) . Some types of block valves have an internal temperature sensing bulb.The external equalizer line connects the evaporator outlet with the underside of the diaphragm. The pressure in the line creates an upward force on the diaphragm. In a block style expansion valve, there is not a required separate external equalizer line. There is not a separate external equalizer line because the line for the evaporator outlet is routed through the block valve.The ball and rod (8) is attached to the diaphragm and the spring. The spring creates an upward force on the ball and rod.When the force due to the pressure in the capillary tube is greater than the combined forces due to the spring and the pressure in the external equalizer line, the valve opens wider. The opening of valve allows more refrigerant flow. When the force due to the pressure in the capillary tube is less than the combined forces due to the spring and the pressure in the external equalizer line, the valve closes. The closing of valve restricts the refrigerant flow.This metering action allows only the required amount of refrigerant to be supplied to the evaporator in varying load conditions.