Mazda Training manual - part 268

 

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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. 

 

 

 

 

 

 

 

 

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