Mazda Training manual - part 267

Air Conditioning Fundamentals

TC070-05-01S

6  – REFRIGERATION 
CYCLE 

 

42

High Pressure 

 

 

We will begin the refrigeration cycle at the compressor, located on the 
left side of Figure 23.The compressor draws in low-pressure vapor 
(about 30 psi) from the evaporator and compresses it to about 175 psi. 
A drive belt on the engine turns the compressor pulley, which spins the 
compressor when its magnetic clutch is engaged. The system monitors 
refrigerant pressure and activates the compressor only when needed. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The compressor pushes this vapor through the outlet to the condenser. 
(The expansion valve is the “plug” in the circuit that allows pressure to 
build on the high-pressure side of the system.) This hot, high-pressure 
vapor carries heat picked up in the evaporator, as well as additional 
heat from the increased pressure provided by the compressor. At this 
point, the refrigerant may be as hot as 130° F (54° C). 

 

 

 

 

 

 

 

 

 

FIGURE 23 The 
compressor draws 
in warm, 
low-pressure vapor 
from the evaporator 
and pushes out 
highly compressed, 
hot vapor. Pressure 
on the “high side” 
remains elevated 
because the 
expansion valve 
restricts flow in the 
circuit.

 

 

Compressor

 

Condenser

 

Receiver/ dryer

 

Expansion valve

 

Evaporator

 

 

 

 

HEAT 

HEAT

Air Conditioning Fundamentals

TC070-05-01S

6  – REFRIGERATION 
CYCLE 

 

43

 

 

 

 

FIGURE 24. The hot, 
high- pressure vapor 
entering the 
condenser quickly 
cools and turns to 
liquid, releasing 
latent heat of 
condensation. 

Compressor 

Condenser 

Receiver/ dryer 

Expansion valve 

Evaporator

 

 

 

Condensation 

 

The hot, high-pressure vapor from the compressor next enters the 
condenser, as shown in Figure 24. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The refrigerant is now under high pressure (about 175 psi), so its 
boiling point is also higher. In addition, the difference between the 
temperature of the outside air and the refrigerant is great, so the 
refrigerant will quickly release heat to the air flowing over the surface of 
the condenser. The hot gas (approximately 130° F [54° C]) quickly 
cools below its high boiling point. As the vapor condenses to a liquid, it 
releases large amounts of heat (latent heat of condensation).

 

HEAT

HEAT 

Air Conditioning Fundamentals

TC070-05-01S

6  – REFRIGERATION 
CYCLE 

 

44

Airflow across the condenser may decrease when the vehicle is not 
moving or in stop-and-go traffic. To compensate, most A/C systems 
include an electric fan to supply additional airflow when needed. 

 

 

Pressure Reduction 

 

After flowing through the receiver/dryer, which removes moisture and 
contaminants, the liquid refrigerant next enters the expansion valve, as 
shown in Figure 25. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The expansion valve restricts the flow of refrigerant, allowing only a 
small amount to pass through on its way to the evaporator. Refrigerant 
pressure on the high side of the expansion valve can be as high as 250 
psi or more. The expansion valve reduces that pressure to about 30 psi 
on the low side. 

 

 

 

 

 

 

 

 

 

FIGURE 25. The 
expansion valve 
restricts the flow of 
refrigerant, 
decreasing its 
pressure, 
temperature, and 
boiling point.

 

 

Compressor 

Condenser 

Receiver/ dryer 

Expansion valve 

Evaporator 

 

HEAT 

HEAT 

Air Conditioning Fundamentals

TC070-05-01S

6  – REFRIGERATION 
CYCLE 

 

45

 

 

 

 

 

 

 

 

 

 

 

FIGURE 26. In the 
evaporator, the 
refrigerant picks up 
heat from the 
passenger 
compartment and 
changes into a 
low-pressure vapor. 
The compressor 
draws in this warm 
vapor and 
compresses it to 
begin the 
refrigeration cycle.

 

 

Compressor

 

Condenser

 

Receiver/ dryer

 

Expansion valve

 

Evaporator

 

 

 

 

At this low pressure, the temperature of the liquid refrigerant drops from 
about 130° F (54° C) to about 30° F (-1° C), and its boiling point 
decreases. 

 

As the refrigerant passes through the expansion valve, it is atomized, or 
turned into a fine, liquid mist. This process increases the surface area of 
the refrigerant so it will easily absorb heat when it passes through the 
evaporator. 

 

Evaporation 

 

As the refrigerant flows into the evaporator (Figure 26), it is a cold, 
low-pressure liquid mist. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At this low temperature (about 30° F [-1° C]), the refrigerant readily 
picks up heat from the passenger compartment. A blower fan pushes 
warm interior air over the evaporator, where it gives up its heat and 
returns to the passenger compartment as cool air. Since the 
refrigerant’s boiling point is lower, it quickly changes into a vapor, 
allowing it to store large amounts of heat as latent heat of vaporization. 

 

 
 
 
 

HEAT

HEAT