Mazda Training manual - part 265

 

  Index      Mazda     Mazda Training Manual

 

Search            

 

 

 

 

 

 

 

 

 

Content   ..  263  264  265  266   ..

 

 

Mazda Training manual - part 265

 

 

Air Conditioning Fundamentals

TC070-05-01S

5 – AIR CONDITIONING   
COMPONENTS 

 

34

 

EXPANSION VALVE / ORIFICE TUBE 
 
An expansion valve or orifice tube regulates the flow of refrigerant to the 
evaporator. To get maximum cooling potential, the pressure of the liquid 
refrigerant must be lowered before it enters the evaporator. At lower 
pressure, the refrigerant’s temperature and boiling point drop, allowing it 
to absorb more heat as it passes through the evaporator. 
 
 
 
Expansion Valve 
 
Although they perform the same function, expansion valves and orifice 
tubes operate differently. Figure 17 shows a typical expansion valve. 
 
 

 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
A bulb        on the evaporator sends information about evaporator 
temperature through a capillary tube        . This tube is attached to the 
diaphragm    on the expansion valve.  
 
If the evaporator becomes too cold, the diaphragm pulls the 
needle-shaped pintle    , closing the valve   and restricting refrigerant 
flow. As the evaporator temperature rises, the diaphragm presses down 
on the pintle, opening the valve and letting more refrigerant through. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

FIGURE 17. The 
expansion valve 
restricts the flow 
of refrigerant to 
the evaporator. 
Lowering the 
pressure of the 
refrigerant allows 
it to absorb more 
heat as it passes 
through the 
evaporator. 
 

Diaphragm 

Capillary tube 

Temperature- 
sensing bulb 

Valve 

Pintle  

Pressure 
spring

 

Air Conditioning Fundamentals

TC070-05-01S

5 – AIR CONDITIONING   
COMPONENTS 

 

35

 

 
 
 
 
 
 
 

FIGURE 18. An 
orifice tube 
restricts refrigerant 
flow between the 
high- and 
low-pressure sides 
of the A/C system. 
 

Pipe caulking 

O-rings 

Cooler pipe 

Mesh screen 

Orifice tube 

 

 

Orifice Tube 

 

Like an expansion valve, an orifice tube divides the high-and 
low-pressure parts of the A/C system. Figure 18 shows a typical orifice 
tube. 

 

 

 

 

 

 

 

 

 

 

 

 

 

The orifice tube has a fixed opening. The flow rate of the refrigerant 
through the opening is determined by the cycling of the compressor clutch. 
In response to changes in temperature and pressure, the clutch turns on 
and off to engage the compressor. 
 

Low Pressure Liquid 
To Evaporator

 

High Pressure Liquid 
From Condeser

 

Air Conditioning Fundamentals

TC070-05-01S

5 – AIR CONDITIONING   
COMPONENTS 

 

36

EVAPORATOR 
 
The evaporator (Figure 19) is located under the dash. It removes heat 
from the passenger compartment and transfers it to the refrigerant. 
Refrigerant enters the evaporator as a cool, low-pressure liquid mist, 
which circulates through the evaporator’s tubes and fins (much like 
coolant circulates through an engine’s radiator). 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
The blower fan forces warm air from the vehicle’s interior over the 
surface of the evaporator. The refrigerant absorbs this heat as it 
changes from a liquid to a vapor (latent heat of vaporization). The 
refrigerant then exits the evaporator as a warm, low-pressure vapor. 
 
 
 

 
 
 
 
 
 
 
 

FIGURE 19. The 
evaporator removes 
heat from the 
passenger 
compartment and 
transfers it to the 
refrigerant as latent 
heat of vaporization

.

 

 
 

 

Air Conditioning Fundamentals

TC070-05-01S

5 – AIR CONDITIONING   
COMPONENTS 

 

37

 
 
 
 

 
 

FIGURE 20. The 
accumulator is 
located after the 
evaporator and 
before the 
compressor on the 
low-pressure side of 
the AC system. 

 

To compressor 
suction line 

From evap. core 

Clutch cycling 
pressure switch 

Low pressure 
service port 

 

 
 
 
 

ACCUMULATOR 
 
The accumulator (Figure 20) is used in AC systems with an orifice tube. 
The accumulator is located after the evaporator and before the 
compressor, on the low-pressure side of the AC system. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

The accumulator functions very much like the receiver/dryer in an 
expansion valve system. However, the receiver/dryer is located on the 
high-pressure side of the system, between the compressor and 
condenser. 

 

 

 

 

 

 

 

 

Content   ..  263  264  265  266   ..