The additional heater unit is connected
to the vehicle electrical system through connector
D22.
This connector, pin 2, receives a direct
supply through the line protected by the maxifuse
B37,
which also supplies the diesel pre-heating system and by a specific
fuse B38; pin 3 is earthed.
Pin 1 of
D22 is connected to
the outside air temperature sensor K79 which, in
turn, receives the reference supply from the alternator (D+ pin
signal): in this way the signal for the outside temperature is only
sent to the additional heater control unit if the engine is running.
The additional heater control unit is equipped
with an autodiagnostic system which can be used: by connecting the
unit to connector
R10: it receives signals from pin 4
of D22 via the diagnostic line.