Aston Martin DB7 Workshop Manual page 350

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Air Conditioning
Portable Diagnostic Unit - Signal Definitions
Reference Signal
(REF)
A/CCM Pin 7 ref Pin 6
This is the main reference signal for the A/CCM. All the sensors reference against
this voltage. Drift in this signal w i l l cause inconsistent temperature control.
Normal voltage should read 2.885 ±10 millivolts
Temperature Demand
(TEMPDEM)
Temperature demand control either selects the required temperature of the system
(auto mode) or the outlet temperature of the vents (manual mode). Pin 35 will vary
from 0 volts at full cooling up to 2.885 volts at full heating.
Note: When defrost is selected, the signal at pin 35 is ignored. The system will go into full
heating through the upper flaps only.
Upper Servo Feedback Potentiometer
(USERFB) A/CCM Pin 30 ref Pin 6
The feedback signal informs the control module ofthe exact position of the flaps,
enabling accurate control o f t h e flap position.
Defrost - Lower flap signal should read 2.9 volts (flap closed, the upper flap
signal should read 1.9 volts.
Max Temperature - Lower flap signal should read 1.14 volts, upper flap signal
should read 1.9 volts.
Min Temperature - Both upper and lower flap signals should read 1 30 ±80
millivolts.
Note: If the feedback sticks low, with the fan continually running, suspect an open circuit
in the 5 volt supply to the feedback potentiometer or the potentiometer itself
Water Switch
(WATSW)
Water Valve
(WATVAL)
A/CCM Pin 21 ref Pin 6
The water switch monitors the temperature ofthe coolant and inhibits heating by
restricting fan operation at coolant temperatures below 30 degrees Celsius. This
enables the vehicle to warm up at a faster rate. It can be overridden by selecting
Defrost.
A/CCM Pin 1 7 ref Pin 6
The water valve controls thef low of hot coolant to the heater matrix. When manual
full cooling is selected, the valve w i l l close inhibiting the heating effort o f t h e
matrix, thus enhancing the cooling effect
Full cooling selected; pin 1 7 should read 10+volts and the water valve should be
closed.
All other conditions, pin 1 7 should read below 0.5 volts and the water valve should
be open.
May 1996 8-73