WD Catalog 2018

4-12

Chapter 4

– Air Conditioner Components

Sometimes refrigerant that leaves the condenser is part liquid and part vapor.

When this happens the receiver-drier acts as a separator. The liquid refriger-

ant settles to the bottom of the tank where the pickup tube inlet is located.

Receiver-driers vary in size and shape and many have a sight glass to aid in

system diagnosis and charging. A sight glass may include a moisture indicator

to let you know if the system is contaminated with moisture. There are high

capacity units, variations in mounting location, fitting types, and the number

and position of filter elements for receiver-driers.

The preferred receiver-drier design for heavy duty vehicle applications is

shown in Figure 4-8. Sandwiched between the two metal baffles are a screen,

two fiberglass filter pads, and at least ten cubic inches of desiccant. In this

design the desiccant is squeezed between the two filter pads. This helps

prevent movement of the molecular sieve material as the refrigerant flows

through. As a result, there is less chance of desiccant breakdown and loose

material reaching and blocking the expansion valve.

AC system design may include single or multi function pressure switches, a

pressure relief valve or fuse plug. These are usually mounted on or connected to

the receiver-drier.

Accumulator

Some AC systems use an accumulator for temporary refrigerant storage in-

stead of the usual receiver-drier. An accumulator is located close to the evapo-

rator outlet and stores excess refrigerant before it moves on to the compressor.

When an accumulator is used instead of a receiver-drier, the typical expansion

valve is replaced with an expansion tube (also called a fixed orifice tube).

An expansion tube allows refrigerant to flow continuously through the

evaporator. At times the refrigerant does not all change to gas and may enter

the accumulator as a liquid. The accumulator prevents liquid refrigerant from

going to the compressor. The pickup tube opening inside an accumulator is at

the top as shown in Figure 4-9.

CAUTION

Serious damage results when liquid is sucked into the

compressor.