Right vent temperature sender -G151
Location, Fig.: N87-0806
A Connector of
temperature sensor -G151
1 - Right vent
temperature sender -G151
The air conditioner is
regulated within an overall temperature range between 18°C and 28°C. However,
the possibilities of individual climate settings for each selectable position
must be set against the fact that the climate zones are not physically
separated from each other.
In the selected
automatic function the air conditioner uses the sensors to determine how much
the air for the climate zone concerned needs to be heated or cooled in order to
deliver the selected temperature.
In this, the air
conditioner control unit determines the flow rate of the engine coolant in the
heating circuit through the heat exchangers or the cooling power of the
refrigerant circuit, as appropriate. The air conditioner control unit decides
according to the requirement, for example that the regulated warm or cooled air
for ventilation is routed to the "driver" and "front
passenger" climate zone and, with the (optional) 4-zone air conditioner,
to the left and right rear passengers.
The design layout with
two adjacent heat exchangers provides a right/left split of the passenger
The temperature of these
two air flows for the left and right halves of the vehicle is primarily
determined by the temperature setting at the front seat positions.
The right vent
temperature sender -G151 is located in the heater/air conditioner unit behind
the right side heat exchanger in the air vent duct to the right footwell.
The air flowing out of
the heater/air conditioner unit into the passenger compartment is recorded with
a temperature-sensitive resistor and so is available as an influencing variable
in the temperature monitoring and control function of the operating and display
unit -J255. The temperature sender -G151 is designed as an NTC sensor. The
resistance is evaluated as a signal from the control unit and regulates the air
distribution and delivery rate of the blower.
J The value of
the out-flow temperature is determined as a reference signal to the dash panel
temperature sensor -G56 on the right and left sides.
J As the
temperature falls the electrical resistance increases.
J The sender is
self-diagnosis compatible. A fault detected in the sender is only registered by
the operating and display unit -J255 if the coolant temperature is detected as
J If the fault:
"short to earth" is detected by the operating and display unit -J255,
the value 150°C is entered in display zone 2 of measured
value block 017.
J If the fault:
open circuit/short to positive is detected by the operating and display unit
-J255, the value -70°C is entered in display zone 2 of measured
value block 017.
J If the right
vent temperature sender -G151 fails, the value of the intact vent temperature
sender -G150 is adopted. Operation is maintained.
J If both
senders (-G150 and -G151) fail, the air temperature downstream of the heat
exchangers can no longer be recorded and the temperature control fails. This
causes the heating power to be controlled in preset temperature increments by
the operating and display unit -J255, using a substitute value for each side.
shows that temperature senders are the most frequent cause of temperature
control faults. They do not usually fail immediately, but deliver false values
to the control unit based on an additional wire resistance as a result of
damage or corrosion in the connector contacts. Thus a comparison of the values
of both senders (-G150 and -G151) in the relevant display zones is recommended
for optimum diagnosis.
J A Air
conditioner; Rep.Gr. 87; Removing and installing right vent temperature sender
J A Current flow
Measured value block 017
Display zone 1:
Readout of left vent
temperature sender -G150 in °C
Display zone 2:
Readout of right vent
temperature sender -G151 in °C
Display zone 3:
Readout of centre vent
temperature sender -G191 in °C
Display zone 4:
Display zone currently