Aston Martin DB7 Workshop Manual page 347

Air Conditioning
Portable Diagnostic Unit - Signal Definitions
^ ^ P
Ground Voltage
(GND2)
Ground Voltage
(GND38)
Ground Voltage
(GND45)
Ground Voltage
(GND6)
High Speed Relay Drive
(HSREL)
In-Car Sensor
(ICSEN)
A / C C M P i n 2 r e f P i n 6
A/CCM Pin 38 ref Pin 6
A/CCM Pin 45 ref Pin 6
A/CCM Pin 6 ref Battery -ve
The four ground signals above must be at battery negative voltage at all times.
A/CCM Pin 16 ref Pin 6
The high speed relay drive signal is used to energise the high speed relay and to
run the blowers at full speed, bypassing the normal fan control circuit. The high
speed relay will be energised whenever Defrost or High speed Fans is selected.
Relay energised, pin 16 should read 10+ volts
Relay de-energised, pin 16 should read below 0.5 volts.
If the signal at pin 16 is correct but only one fan responds, suspect a fault in the
harness or relay.
A/CCM Pin 4 ref Pin 6
The in-car temperature sensor operates in the range 0-5 volts. Actual output is
2.732 volts at 0 degrees Celsius ±0.01 volts for every degree Celsius above or
below zero. The sensor signal forms a reference point for the whole system.
If the signal on this pin remains at less than 1 volt, suspect either a short to ground
on the signal wire or an open circuit on the 5 volt supply line to the sensor.
If the signal rises to approximately 3 volts, then suspect an open circuit on the
ground supply to the sensor.
8-70
May 1996