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