Centre vent temperature sender -G191
Location, Fig.: A87-0548
A Connector of
temperature sensor -G191
B Centre vent
temperature sender -G191
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 centre vent
temperature sender -G191 is located in the centre air outlet duct in the air
distribution housing in the middle of the dash panel at the front.
The air flowing out of
the right and left side air ducts from the heater/air conditioner unit through
the heat exchangers is mixed in the air distribution housing in the middle of
the dash panel and recorded with the 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. Depending on the flap
setting, the air is routed to the two centre vents for direct ventilation and
to the vents in the top of the dash panel for indirect ventilation. The
temperature sender -G191 is designed as an NTC sensor. The resistance is
evaluated as a signal from the control unit and regulates the air temperature
to the centre left and right vents.
J As the
temperature falls the electrical resistance increases.
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 3 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 3 of measured
value block 017.
J If the centre
vent temperature sender -G191 fails, operation is maintained.
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 with the
values of senders -G150 and -G151 in the relevant display zones is recommended
for optimum diagnosis.
J A Air
conditioner; Rep.Gr. 87; Removing and installing centre 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