Mazda Training manual — part 262

Air Conditioning Fundamentals

TC070-05-01S

4 – PRINCIPLES OF
REFRIGERATION

22

Principle Six: Compressed Vapor

The sixth and final principle states that when you compress a vapor, its
pressure and temperature will increase even though you add no heat.
The refrigerant vapor in an automotive air conditioning system is
compressed to as much as 250 psi or more. This raises the temperature
of the vapor, as well as the boiling and condensation points. Figure 8
shows this principle in action.

As the illustration shows, if you compress a refrigerant from 30 psi to
175 psi, the vapor temperature increases from 32° F (0° C) to 130° F
(54° C). At the same time — according to Principle Five — the boiling
point and condensation point of the vapor also increase, since the vapor
is under higher pressure.

This increase in the temperature of the compressed vapor is not due to
any increase in heat stored in the vapor. If you remove heat from the
130° F (54° C) vapor, it will condense into a liquid without changing
temperature. The heat given up during this change of state is the latent
heat of condensation. Moreover — according to Principle Four — the
temperature of the refrigerant will not decrease until the entire vapor
condenses into liquid.

FIGURE 8. When a
vapor compresses,
its temperature
and pressure
increase without
heat being added.

Vapor @ 30 psi.
32° F (0° C)

Vapor @ 175 psi,
130° F (54° C)

Compressor

Intake side

Vapor

Discharge side

Air Conditioning Fundamentals

TC070-05-01S

4 – PRINCIPLES OF
REFRIGERATION

23

REVIEW EXERCISE 3

Fill in the words that correctly complete these sentences. Check your answers with the
answer key on page 26.

1. As a substance changes state from a liquid to a vapor, it stores a large amount of heat

energy without a rise in temperature. This process is called the
______________________________________.

2. Principle One states that heat flows from ____________________ to

____________________ when objects are in contact or connected by a good heat
conductor.

3. If you lower the pressure of a liquid, the boiling point of the liquid

____________________.

4. If you compress a vapor, its temperature ____________________.

5. When a vapor changes back into a liquid, it ____________________ heat without

changing temperature.

6. If you freeze five pounds of water, the resulting ice block will weigh

____________________ pounds.

7. If you lower the pressure of a compressed vapor, its temperature

____________________.

Air Conditioning Fundamentals

TC070-05-01S

5 – AIR CONDITIONING
COMPONENTS

24

OBJECTIVES

After completing this section, you will be able to identify and describe the function of the
following A/C components:

• Compressor

• Condenser

• Receiver/Dryer

• Expansion

Valve

• Orifice

Tube

• Evaporator

• Accumulator

Air Conditioning Fundamentals

TC070-05-01S

5 – AIR CONDITIONING
COMPONENTS

25

FIGURE 9. A
typical automotive
A/C system
includes:

Compressor

Condenser

Receiver/ dryer

Expansion

valve

Evaporator

Answers to
Review Exercise 3

1. latent heat of

vaporization

2. hot to cold

3. decreases

4. rises

5. releases

6. five

7. decreases

OVERVIEW


Figure 9 shows the major components in an automotive A/C system.





















These components circulate refrigerant, which constantly changes state
from a:

Warm, low-pressure vapor entering the compressor

Hot, high-pressure vapor entering the condenser

Warm, high-pressure liquid entering the receiver/dryer

Cold, low-pressure liquid exiting the expansion valve

Cold, low-pressure liquid entering the evaporator

These changes of state and temperature transfer heat from the
passenger compartment of the vehicle to the outside air. The following
topics describe each component in detail.

HEAT

HEAT