Mazda Training manual - part 261

 

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Mazda Training manual - part 261

 

 

Air Conditioning Fundamentals

TC070-05-01S

4 – PRINCIPLES OF   
REFRIGERATION 

 

18

Principle Two: Temperature and Mass 

 

According to Principle Two, the mass of an object remains the same 
regardless of its heat content. For example, the pan of water in Figure 
3 weighs one pound whether it is at its freezing point or boiling point. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Principle Three: Latent Heat of Vaporization 

 

Principle Three states that when matter changes from a liquid to a 
vapor, it absorbs a large amount of heat without changing 
temperature. 

 

 

Figure 4 illustrates this principle. At sea level, water exists as a liquid 
between 32° and 212° F (0° and 100° C). At exactly 212° F (100° C), 
water can be either a liquid or a vapor, depending on how much heat it 
contains. By adding more heat to the water, you can eventually 
convert it to steam, but the temperature of the steam will remain 212° 
F (100° C). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 

 
 
FIGURE 3. Principle 
Two 
– The mass of an 
object remains the 
same regardless of its 
temperature.

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

FIGURE 4. Principle 
Three 
– When matter 
changes from a liquid 
to a vapor, it absorbs 
large amounts of heat 
without changing 
temperature

 

 

 

212°F

1 lb. water

1 lb. water

 

Add heat 

Solid 

Liquid

Vapor 

Remove heat 

Air Conditioning Fundamentals

TC070-05-01S

4 – PRINCIPLES OF   
REFRIGERATION 

 

19

 
 
 
 
 
 

FIGURE 5. The 
latent heat of 
vaporization is 
heat stored in a 
substance as it 
changes state 
from a liquid to a 
vapor

.

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Figure 5 illustrates the latent heat of vaporization. Assume you had a 
pound of water that was 212° F (100° C), but still a liquid. To change the 
liquid water into steam, you would have to apply 970 British Thermal Units 
of heat. Eventually, you would create a pound of steam that would still 
have a temperature of 212° F (100° C). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
As steam, the pound of water would have absorbed 970 BTUs of energy 
without any change in temperature. This “latent” heat absorption is the 
basis for modern refrigeration systems. 

 

In an A/C system, latent heat of vaporization occurs within the evaporator. 
When the refrigerant passes through the evaporator, it absorbs heat from 
inside the vehicle and begins to boil. As heat continues to be absorbed, 
the refrigerant changes from a low-pressure liquid into a low-pressure 
vapor.

212°F 

212°F 

1 lb. water 

1 lb. steam 

970 BTUs 

Air Conditioning Fundamentals

TC070-05-01S

4 – PRINCIPLES OF   
REFRIGERATION 

 

20

Principle Four: Latent Heat of Condensation 

 

Principle Four is the reverse of Principle Three. When a vapor cools 
enough to change into a liquid, it releases the latent heat stored while it 
was changing into a vapor. The process of changing from a vapor to a 
liquid is called condensation, so the heat released in this change of state 
is the latent heat of condensation
Figure 6 illustrates this principle. 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 

In this example, the pound of steam is cooling to its dew point (the 
temperature at which it turns back into liquid). As the water changes 
state, it releases 970 BTUs. Notice that the pound of water remains at 
212° F (100° C) even though it has released a large amount of heat. 

 

In an A/C system, latent heat of condensation occurs within the 
condenser. The condenser discharges heat from the refrigerant into the 
outside air. As the refrigerant cools, it condenses from a high-pressure 
vapor to a high-pressure liquid. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 

 
FIGURE 6. The 
latent heat of 
condensation is 
heat released from 
a substance as it 
changes state from 
a vapor to a liquid. 
 

212°F 

212°F 

1 lb. water 

1 lb. steam 

970 BTUs 

Air Conditioning Fundamentals

TC070-05-01S

4 – PRINCIPLES OF   
REFRIGERATION 

 

21

 

 

 

 

 

 

 

 

 

 

 

FIGURE 7. To 
increase the 
boiling point of a 
liquid, increase 
its pressure. To 
decrease the 
boiling point, 
decrease the 
pressure.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Principle Five: Pressure and Boiling Point 

 

Principle Five states that changing the pressure of a liquid or vapor 
changes its boiling point. Higher pressure increases the boiling point, 
while lower pressure decreases the boiling point, as shown in Figure 7. 
An auto air conditioning system uses this principle to remove heat from 
the interior of the vehicle. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Previously, we compared boiling water at sea level and at the top of 
Pike’s Peak. At sea level, water boils at 212° F (100° C). The lower 
atmospheric pressure at Pike’s Peak allows water to boil at only 187° F 
(86° C). 

 

Figure 7 shows what happens if you increase the pressure of the water. 
At the higher pressure shown in this figure, water will have to reach 260° 
F (127° C) before it boils.

Boiling point 

260°F 

212°F 

Boiling point

 

 

 

 

 

 

 

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