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9.9 Hot/cold mix
The control of the hot/cold mix depends on the
system architecture.
In most cases the HVAC is designed with an air
mixing solution, but the temperature can also be
controlled by the water flow rate in the heater core.
9.9.1 By air mixing
In manual air conditioning systems, the air is mixed
using flaps inside the HVAC. The flaps are actuated
from the control panel using cables.
Automatic air conditioning systems apply the same
principle, but they are fitted with motor-driven
mixing flaps.
The mix of hot and cold air is permanently
adjusted in order to regulate the temperature
in the cabin to the set point.
9.9.2 By adjusting
the hot water flow
Some systems can adjust the hot temperature by
acting on the flow rate of hot water in the heating
radiator.
This variant exists in both manual and automatic
air conditioning systems and uses either a mecha-
nical valve controlled by a cable, or electrovalves
controlled by the air conditioning ECU
.
The mixing function
is located inside the HVAC
at the junction of hot and
cold air streams
9. The Heating
Ventilation and
Air Conditioning
unit (HVAC)
30
Mechanical control panel
(via a bowden cable)
Flow control via a mechanical tap
inlet
A/C control unit
(PWM controlled)
Flow control via an electro-actuator
inlet
Heat control in the heater core