Reference Signal

Reference Signal

(REF) A/C CM Pin 7 ref Pin 6

This is the main reference signal for the A/C CM. All the sensors reference against this voltage. Drift in this signal will 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/C CM Pin 30 ref Pin 6

The feedback signal informs the control module of the exact position of the flaps, enabling accurate control of the 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 130 ±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) A/C CM Pin 21 ref Pin 6

The water switch monitors the temperature of the 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.

Water Valve

(WATVAL) A/C CM Pin 17 ref Pin 6

The water valve controls the flow of hot coolant to the heater matrix. When manual full cooling is selected, the valve will close inhibiting the heating effort of the matrix, thus enhancing the cooling effect

Full cooling selected: pin 17 should read 10+ volts and the water valve should be closed.

All other conditions, pin 17 should read below 0.5 volts and the water valve should be open.