Damper Motors; Fan Control - Volvo 850 Supplement Manual

temperature control dial, and engine coolant temperature.
At low outside temperatures, the ECC control module selects
floor/defrost setting, with a slight amount of bi-level air if
sunshine is present. If outside temperature is between 50-66
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19 C), a varying degree of bi-level air is selected. At temperatures
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greater than 68 F (20
vents.
The ventilation air distribution setting is selected if
driver's side control panel is set for maximum cooling. The
floor/defrost setting is selected if maximum heating is selected.
The defrost air distribution setting is selected if engine is
cold and outside and interior temperatures are also low. This changes
to varying degrees of floor/defrost air distribution as engine coolant
temperature increases. The transition from defroster to
floor/defroster setting takes place more quickly in sunshine.
AIR TEMPERATURE SENSORS & SOLAR SENSOR
Two interior temperature sensors and 2 duct temperature
sensors are required for individual temperature control of driver's
and passenger's sides. Each interior temperature sensor incorporates a
fan which draws air through sensor.
The resistance of the air temperature sensors decreases as
temperature increases. The solar sensor, combined with the theft alarm
diode, is a photodiode which generates a current when exposed to solar
radiation.

DAMPER MOTORS

The temperature control damper motors, recirculation damper
motor, floor/defroster damper motor, and ventilation damper motor are
all identical, but their control range varies according to the damper
being controlled.
The damper motors have a position sensor to enable the ECC
control module to determine damper position, learn the damper limit
positions, and to detect any fault in damper motor. The ventilation
damper is operated by damper motor through 2 gear segments; one fitted
to damper motor shaft and the other on ventilation damper shaft.

FAN CONTROL

Heater (blower motor) fan speed is variably controlled by ECC
output (power) stage in response to signals from ECC control module.
The ECC control module digital control signals vary in length
according to required fan speed.
The ECC output stage has an electronic unit which receives
the digital control signals and converts them to voltage. If there is
no control signal or the fan is disabled, the ECC output stage sends a
diagnostic signal to inform the ECC control module of the fault.
If fan speed control lever is set to AUT (automatic) mode,
fan speed is influenced by the position of driver's side temperature
control dial, driver's side interior temperature sensor, vehicle
speed, and engine coolant temperature.
The highest fan speed is selected if driver's side
temperature control dial is set to maximum or minimum cooling or
heating. The greater the difference between the desired and actual
temperatures, as sensed by the driver's side temperature sensor, the
higher the fan speed.
As vehicle speed increases, the fan speed will be reduced to
maintain a constant airflow throughout the passenger compartment. When
heating the passenger compartment after starting a cold engine, the
fan speed is gradually increased as engine coolant temperature rises.
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C), all air is directed to instrument panel
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F (10-