Mazda Training manual - part 273

Air Conditioning Fundamentals

TC070-05-01S

9  – AIR DISCHARGE 
MANAGEMENT 

 

66

If the fresh air door is open, a certain amount of “ram” air enters as the 
vehicle moves down the road. In most cases, this is not enough to 
provide noticeable airflow in the passenger compartment. The blower 
fan ensures that plenty of airflow is available for cooling and heating. 

 

 

 

Temperature Blend Door 

 

The temperature blend door, highlighted in Figure 34, controls airflow to 
the evaporator and heater. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The temperature blend door can be set to any position along the arc of 
its travel. With the system set to the “cool” position, the temperature 
blend door blocks all airflow to the heater. When the door is partially 
open, the air discharged into the passenger compartment is a 
combination of heated air, unheated air, and cooled air. Proper 
adjustment of the temperature blend door is critical to system 
performance. 

 
 
 
 
 
 
 
 
 
 
 
 

FIGURE 34. The 
temperature blend 
door directs airflow 
to the evaporator, 
the heater, or to 
both units.

 

Heater

 

Evaporator

Temperature blend door

Air Conditioning Fundamentals

TC070-05-01S

9  – AIR DISCHARGE 
MANAGEMENT 

 

67

 
 
 
 
 
 
FIGURE 35. The 
defroster door opens 
to let airflow on the 
windshield. At the 
same time, doors to 
the floor and upper 
vents close.

 

Defroster Door 

 

The defroster door redirects all airflow to the windshield. Figure 35 
shows the defroster door. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
When the operator selects the defrost position, a door blocking the 
defroster passages opens, and other doors for the floor and upper vents 
close. This arrangement provides maximum airflow to the windshield 
area. 

 

System operation depends on the correct adjustment of the defroster 
door. If incorrectly adjusted, the defroster door may open, allowing 
unintended airflow to the windshield. 
 

Vent doors 
(closed)

 

Heater   Evaporator

Defroster door

Air Conditioning Fundamentals

TC070-05-01S

9  – AIR DISCHARGE 
MANAGEMENT 

 

68

Vent/Face and Heater Doors 

 

The vent/face and heater doors (Figure 36) direct air either to the floor 
vents or the upper vents. If the operator selects the “bi-level” position, 
air will flow to both sets of vents.

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 

FIGURE 36. The 
vent/face and heater 
doors direct airflow 
to the upper or 
lower vents. In 
“bi-level” position, 
air flows to both 
sets of vents.

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 

Evaporator

Vent doors

 

Heater

 

Defroster door

Air Conditioning Fundamentals

TC070-05-01S

9  – AIR DISCHARGE 
MANAGEMENT 

 

69

REVIEW EXERCISE 9 
 
Match each component on the left to one of the descriptions on the right. Check your 
answers with the answer on page 72. 
 
1. 

Vent/face and heater doors 

 
2.   Defroster door 
 
3.   Fresh/re-circulated air door 
 
4.   Temperature blend door 
 
5.   Blower fan 
 
 
 
 
 
 
 
 

A.    In bi-level position, allows air flow to 

upper and lower vents 

 
B.    Draws air over evaporator and/or 

heater 

 
C.    Directs air flow to evaporator, 

heater, or both 

 
D.    Opens to allow maximum air flow 

to windshield 

 
E.      Allows outside air into heating and 

A/C system