WD Catalog 2018

5-5

Go to Chapter Start

These controls are designed to meter refrigerant flow through the evapo-

rator coil. Thermostat and compressor clutch function are independent of

these refrigerant flow control devices.

Note:

A thermostat or pressure switch controls the com-

pressor clutch assembly. Automatic refrigerant me-

tering devices sense pressure/temperature in the sys-

tem and control refrigerant flow through the evapora-

tor. The combination of controls keeps the system

balanced so that heat energy can move efficiently by

taking advantage of natures laws. When the system is

out of balance, refrigerant may move too fast or too

slowly. It will not absorb enough heat to cool the cab

properly, or may result in too low a temperature in

the evaporator. In some cases, the normal condensa-

tion collecting on the evaporator fins may freeze in-

stead of draining out of the cab. The frozen conden-

sate will block air flow through the evaporator. No air

flow—no cooling.

Many truck and off-road vehicles have control variations, combinations

and supplemental controls. We will explain these controls after we de-

scribe basic and automatic heater controls.

Figure 5-4

This group of illustrations

notes how the most fre-

quently used refrigerant

metering or flow control

devices function.

Air Conditioner Controls

EXPANSION TUBE HAS

NO MOVING ELEMENT

ELECTRICALLY CON-

TROLLED FREON SOLENOID

VALVE

PRESSURE CONTROLLED

BLOCK TYPE TXV

TYPICAL PRESSURE CONTROLLED

TXV (EXTERNALLY EQUALIZED)