WD Catalog 2018

4-4

Chapter 4

– Air Conditioner Components

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Table of Contents

Index

All PAG-based lubricants are not necessarily the same. Different compressor

manufacturers use different additives. Unlike the mineral oil lubricant for

R-12, you may need to keep several different lubricants on hand for use with

R-134a.

In retrofit systems use that lubricant recommended by the compressor

manufacturer.

Lubricants that come out of an air conditioning system should never be

reused. Contaminants and moisture are probably contained in such material.

Compressors

When a compressor is engaged and driven by the engine through the clutch

pulley, the compressor functions as a pump to move refrigerant and refrigeration

oil around the AC system. The compressor pistons move back and forth within

their cylinders as the compressor shaft revolves. A special lubricating oil is used

for each AC compressor. This oil, called refrigeration oil, is formulated to be

moisture free and compatible with the refrigerant used. It circulates throughout

the AC system. The lubricant used with R-12 is not compatible with R-134a.

We generally refer to an AC system as having a suction or low (pressure) side

and a discharge or high (pressure) side. The two sides of the system are divided

at the compressor, and at the expansion valve (refrigerant metering device)

located at the inlet to the evaporator.

The compressor pulls refrigerant gas from the evaporator, through the low

pressure suction hose, the inlet service valve and one way reed valves, and

into the compressor. During compression strokes, refrigerant gas is forced out

of the compressor through more one way reed valves, an outlet service valve

and a high pressure discharge hose to the condenser. The pressure from

compressor action moves the refrigerant through the condenser, receiver-drier

and connecting hoses to the expansion valve. Figure 4-3 shows typical com-

pressor function in the AC system. Note the parts of the system under high

and low pressure.

DOWN

INLET

OUTLET

PISTON ON

DOWNSTROKE

AND

UPSTROKE

COMPRESSOR INLET IS SUCTION SIDE (LOW

PRESSURE) – COOL LOW PRESSURE GAS

SUCKED IN FROM EVAPORATOR

COMPRESSOR OUTLET IS DISCHARGE SIDE

(HIGH PRESSURE) – HOT HIGH PRESSURE GAS

FORCED OUT TO THE CONDENSER

We deliver power to the compressor through the clutch pulley. The pulley is

driven by a V-belt connected to another pulley powered by the truck engine.

The location of the compressor relates to the truck design and options, avail-

able space under the hood, and the AC system components selected.

Figure 4-3

In these drawings of a two-

cylinder compressor the

suction or low pressure side

and discharge or high pres-

sure side are noted in a

cutaway view.