Condenser Fans
The HEVAC panel provides a signal normally at 12
volts for “off” condition and 0 volts for the “on”
condition, which in the case of petrol vehicles is fed
into the ECM and diesel vehicles directly onto the
coil of relay 18. In line is the Air–Conditioning
pressure switch 2, which turns the fans on/off.
When relay 18 is energised, it provides connection
between relays 13 and 14 (fan 1 and 2) in series or
parallel with each other. This is dependent upon the
state of the air–conditioning pressure switch 1.
For the petrol option, when the signal enters the
ECM, the ECM will switch the output on/off to the
fusebox. The ECM will switch the output on
sometimes for engine cooling reasons even though
the engine has been turned off.
Heater Core Sensor
This sensor measures the engine coolant
temperature within the fascia area.
Evaporator Sensor
This sensor is located within the evaporator unit and,
by providing feedback to the HEVAC ECU, prevents
it from freezing.
Alternator Charge signal
This signal is given to the HEVAC ECU to inform it
that the engine is running. This signal is active low.
Diagnostic K line
This line is used to communicate with the diagnostic
equipment (TESTBOOK) and is normally held at 12V
when not active.