WD Catalog 2018

4-13

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OUTLET

INLET

PICKUP TUBE

LIQUID BLEED HOLE

FILTER SCREEN

DESICCANT BAG

CONNECTOR FOR PRESSURE

SWITCH IF USED

Most AC systems with an accumulator have a thermostat to control the clutch.

The thermostat is usually positioned to sense refrigerant temperature between

the evaporator outlet and the accumulator. Some AC systems with an accumu-

lator have a pressure switch mounted on the accumulator to control the

compressor clutch.

Expansion Valves & Other Metering Devices

Various types and designs of refrigerant metering or control valves are used in

AC systems. The valves are actuated by temperature and/or pressure. All are

designed to control the flow of refrigerant into and/or out of the evaporator or

compressor.

In addition to the block type expansion valve shown and described in

Chapter 2

, Figure 2-7, there are other valve designs. The types of expansion

valves discussed in this section are:

Thermostatic Expansion Valves

Expansion Tubes

1. Thermostatic Expansion Valves

The traditional internally and externally equalized expansion valves each

work the same way. Valve function is controlled by temperature and

pressure of the refrigerant gas as it leaves the evaporator on it’s way back

to the compressor. A small diameter hollow tube (capillary tube) is at-

tached to the top of the valve diaphragm housing.

The capillary tube contains a small amount of gas or liquid such as

refrigerant. The coil or bulb at the end of the tube is clamped to the outlet

manifold from the evaporator. The gas in the capillary tube expands and

contracts from heat in the outlet tube. It pushes to open the valve orifice.

Evaporator Coil

Figure 4-9

The accumulator has filter-

ing elements like a receiver-

drier. Parts are named in

this drawing and arrows

show the path refrigerant

follows as it moves through

the accumulator.