Workshop Manuals Factory service & repair Aston Martin
Aston Martin DB7 Factory Workshop Manual Volume 2: Electrics, Body and Air Conditioning (1994-1998)04 · Air conditioning
04 · Heating & A/C

Fault Finding

Make
Aston Martin
Model
DB7 Factory Workshop Manual Volume 2: Electrics, Body and Air Conditioning
Year
1994–1998
Section
System fault diagnosis › Fault Finding
Air conditioningFault Finding

Probable causes of faults can be found by comparing actual system pressures, registered on the manifold gauge set or recovery-recharge-recycle station, and the pressure to temperature relationship graphs found on the previous page. The chart below shows the interpretation that may be made by this difference. The ‘Normal’ condition is that which is relevant to the prevailing ambient and evaporator temperatures.

Note: If erratic or unusual gauge movements are experienced, check the equipment against a known manifold gauge set.

Low Side Gauge High Side Gauge Symptom Diagnosis
Normal Normal Discharge air initially cool then warms up Moisture in system
Normal to low Normal As above As above
Low Low Discharge air slightly cool HFC 134A charge low
Low Low Discharge air warm HFC 134A charge very low
Low Low Discharge air slightly cool or frost build up at expansion valve Expansion valve stuck closed
Low Normal to high Discharge air slightly cool Restriction in High side of system
High Low Compressor noisy Defective reed valve
High High Discharge air warm and high side pipes hot HFC 134A charge high or condenser malfunction
High High Discharge air warm Expansion valve stuck open
Sweating or frost at evaporator

Fault Finding

Caution: The microprocessor is extremely sensitive and should only be tested using a digital multimeter with no less than a 3.5 digit display and a resistance of no less than 2 M ohms. The use of any other form of multimeter will damage the microprocessor irreparably.

Note: Always allow time for the servo motors and blower motors to come to a rest before starting a check.

The car should be in a workshop and the ambient temperature should be stable e.g. 24°C (75°F) for at least 30 minutes before commencing the automatic check.

At 24°C the sensor voltage is 2.972 V ± 2 mV. The rate of change is 10mV per 1°C.

Unless stated otherwise, all checks are carried out at the ECM test plugs

Mode Switch: Off Ignition Switch: Aux 2

Signal Pin No. Voltage
Battery supply 1 11 to 14V
Recirc input 9 0 to 2V
Earth-ground 2 0 to 40mV
Earth-ground 6 0 to 40mV
Earth-ground 10 0 to 40mV
Earth-ground 38 0 to 40mV
Earth-ground 45 0 to 40mV
From mode switch 44 0 to 12V
To mode switch 12 10 to 13.3V

Parts & tools for this job For 1994 Aston Martin DB7

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