Mazda Training manual — part 268

Air Conditioning Fundamentals

TC070-05-01S

6 – REFRIGERATION
CYCLE

46

After picking up heat in the evaporator, the refrigerant gas is drawn into
the inlet side of the compressor, where it begins another refrigeration
cycle.

Orifice Tube System

An orifice tube system works similar to an expansion valve system.
However, since the orifice tube is a fixed size, the tube must flood the
evaporator to work properly under all conditions. As the refrigerant
passes through the evaporator, most of it changes into vapor and then
travels to the accumulator, as shown in Figure 27.

As we discussed before, the accumulator replaces the receiver / dryer
in the system. The accumulator separates the liquid refrigerant from the
refrigerant vapor. This prevents liquid refrigerant from getting back into
the compressor, and allows higher heat loads by keeping the remaining
liquid on hand.

FIGURE 27. As the
refrigerant passes
through the
evaporator, most
of it changes into
vapor and then
travels to the
accumulator.

Compressor

Condenser

Accumulator

Orifice tube

Evaporator

High pressure vapor

Low pressure vapor

High pressure liquid

Low pressure liquid

Air Conditioning Fundamentals

TC070-05-01S

6 – REFRIGERATION
CYCLE

47

Compressor

Condenser

Receiver/ dryer

Expansion valve

Evaporator

REVIEW EXERCISE 6

Use the diagram below to answer the following questions. Check your
answers with the answer on page 50.

1.

At point in the diagram, is the refrigerant pressure high or low?

2.

At point , is the refrigerant a vapor or a liquid?

3.

Is the refrigerant at point hotter or colder than the refrigerant at
point ?

4.

At point , is the refrigerant a vapor or a liquid?

5.

At point , is the pressure of the refrigerant low or high?

6.

At point , does the refrigerant absorb or release heat?

7.

Is the refrigerant at point hotter or colder than the refrigerant at
point ?

8.

At point , is the refrigerant a vapor or a liquid?

HEAT

HEAT

Air Conditioning Fundamentals

TC070-05-01S

7 – REFRIGERANTS

48

OBJECTIVES


After completing this section, you will be able to:

•

Describe the chemical structure and properties of R-12 refrigerant.

•

Describe the chemical structure and properties of R-134a refrigerant.

•

Describe the differences between R-12 and R-134a.

•

Define recycled, reclaimed, and extracted refrigerant.

•

Explain procedures for storing recycled refrigerant.

•

Describe the two approaches for retrofitting older A/C systems.

•

Follow safety procedures and rules when working with A/C systems.

INTRODUCTION TO REFRIGERANTS

Auto air conditioning systems typically use one of two types of refrigerant, either R-12 (in
older vehicles) or R-134a (in newer vehicles). The R stands for refrigerant. Both chemicals
are suitable A/C refrigerants because they have very low boiling points.

Though similar in many respects, R-12 and R-134a affect the environment differently. The

following pages describe these two refrigerants, highlighting the differences between them,
as well as proper storage and handling techniques.

Air Conditioning Fundamentals

TC070-05-01S

7 – REFRIGERANTS

49

FIGURE 28. CFC-12
contains carbon,
fluorine, and
chlorine. It was
commonly used as a
refrigerant until
about 1990.

Answers to Review
Exercise 6

1. High

2. Vapor
3. Hotter
4. Liquid
5. Low
6. Absorb
7. Colder

8. Vapor

CFC-12 (R-12)

R-12 is the common name for Dichlorodifluoromethane-12 (CFC-12), a
chemical used in many types of refrigeration systems up until about
1990.


Chemical Structure

Figure 28 shows the chemical structure of CFC-12. It contains a single
carbon atom, surrounded by two fluorine atoms and two chlorine atoms.
The chemical formula for CFC-12 is CCl2F2

Properties of R-12

R-12 is a suitable refrigerant because of its excellent ability to absorb
large quantities of heat. In addition, R-12:

• Is odorless, tasteless, non-toxic, and non-corrosive.

• Does not damage rubber seals used in the system.

• Is soluble in oil, which is important because the refrigerant carries

the lubricating oil to the A/C system compressor.

• Has a very low boiling point of -22° F (-30° C) at sea level; this

property allows R-12 to absorb and carry off large quantities of heat.

• Has a direct, predictable relationship between its temperature and

pressure, which lets R-12 absorb or release large amounts of heat
in response to changes in pressure.