1997 ASTON MARTIN DB7 AUX

Air Conditioning
Functional Check
Functional Check
This functional check procedure is provided as a simple system validation and is structured to augment the Portable
Diagnostic Unit (PDU).
Stage 1 (Cold engine only, if not proceed to Stage 2)
Procedure Normal System Reaction

1.
Ignition ON
Select MIN temperature, MAN, speed 3, Mid face.
(Engine Stationary) Fans Start

2.
Select MAX temperature Fans continue to run
3. Ignition OFF
Select MAX temperature and defrost
Ignition ON Fans start at maximum speed

4.
Select fan speed
1
Fan speed adjusts accordingly - system OK
Stage 2
Procedure Normal System Reaction

1.
Start up engine and warm up
Select fan speed 1, MAN, MAX TEMPERATURE
and mid face

2.
Open all vents Fans start after 3 seconds

2.
Select fan speed 2 Fan speed increases then stabilises
3. Select fan speed 3 Fan speed increases then stabilises

4.
Select defrost Fan speed steady at high
All air at screen and dash end
5. Re-select fan speed 1
Select AUX ignition key position
6. Slowly select MIN temperature Solenoids switch 1. centre vent

2.
water valve
3. Re-circulation
7. Re-select MID temperature
8. Select DEM Solenoid clicks
Air at screen
9. Select manual re-circulation Solenoid click

10.
Check flap for position

11.
Run Engine to normal temperature

12.
Select: MAN, 3/4 MAX heat and fan speed 2 Air from door vents
cool,

air temp from foot outlet slightly warm

13.
Select MAX temperature and air differential to hot face All vent outlets max temp except screen vent

14.
Select temperature
approx. 1/4 MAX heat and mid face level Cool air from centre vents

15.
Select MIN temperature Blower flaps at re-circulation position
All outlets blowing cold air except screen vent
May 1996 8-15

Air Conditioning
Electronic Control Module r^^?
Description
The ECM (Fig 1) controls the air conditioning
system so that selected temperaturesare maintained.
It cannot be repaired but input and output signals
can be measured, using the PDU, for diagnostic
purposes.
Input-Output Voltage Signals
The following voltage signal levels are input and
output from the ECM:
Digital input levels:
Low
High
Analogue input levels:
General
Blend Flap Potentiometer
Digital output levels
Relays On
Off
Vacuum manifold Pull-in
Drop-out
Analogue output levels
Blend Flap Servo Motors
Blower Motors
0.16 to 1.1V
3.70 to 4.50V
0 to 0.2885 V
0 to 5.0V
8.0V
1.0 to 5.0V
5.6V (typical)
3.5V (typical)
0.5 to 6.5V
0.5 to 2.5V
figure 1.
The ECM
is
turned on when the ignition
is
turned on
to auxiliary position 1. its operating range is 13.5-
14.2 volts.
The ECM power unit supplies +5 volts for the
temperature sensors, feedback potentiometers and
high speed relays.
An integrated circuit protects the ECM against
reversed polarity and voltage surges.
Caution: Take care when connecting test equipment. If
test pins are allowed to be shorted together, to
ground or to positive supplies the ECM will be
damaged.
8-20 May 1996

Air Conditioning
System Fault Diagnosis ^=2?
System Fault Diagnosis
Probable causes of faults can be found by comparing actual system pressures, registered on the manifold gauge set
or recovery-recharge-recycie 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
Normal
Gauge
Normal to low
Low
Low
Low
Low
High
High
High Side Gauge
Normal
Normal
Low
Low
Low
Normal to high
Low
High
High
Fault Finding
High
Symptom
Discharge air initially cool
then warms up
As above
Discharge air slightly cool
Discharge air warm
Discharge air slightly cool or
frost build up at expansion
valve
Discharge air slightly cool
Compressor noisy
Discharge air warm and high
side pipes hot
Discharge air warm
Sweating or frost at evaporator
Diagnosis
Moisture in system
As above
HFC 134A charge low
HFC 134A charge very low
Expansion valve stuck closed
Restriction in High side of system
Defective reed valve
HFC 134A charge high or
condenser malfunction
Expansion valve stuck open
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 lOmVper
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.
Battery supply 1
Recirc input 9
Earth-ground 2
Earth-ground 6
Earth-ground 10
Earth-ground 38
Earth-ground 45
From mode switch 44
To mode switch 12
Voltage
n to 14v
0to2V
0 to 40mV
0 to 40mV
0 to 40mV
0 to 40mV
0 to 40mV
0 to 12V
10 to 13.3V
8-30 May 1996

Air Conditioning
Portable Diagnostic Unit - Signal Monitoring 3^^?
Air Conditioning Signal Monitoring
The following signals can be monitored using the PDU. The abbreviated name of the signal is shown on the PDU
display.
Display Name Full Signal Name
AMBTEMP Ambient temperature sensor
ARECIP Auto-Recirculation input
ARECOP Auto-Recirculation output
AUX+ Auxiliary battery positive
CLUREL Clutch relay drive output
CVSOL Centre vent solenoid
DEFSOL Defrost solenoid
DIFF Temperature differential
EVSEN Evaporator sensor
FANDEF Fanspeed defrost
FANHIG Fanspeed high
FAN LOW Fanspeed low
FANMED Fanspeed medium
FIVEV Five volt supply voltage
FORSERL Lower servo forward drive
FORSERU Upper servo forward drive
GND10 Ground voltage
GND2 Ground voltage
GND38 Ground voltage
GND45 Ground voltage
GND6 Ground voltage
HSREL High speed relay drive
ICSEN In-Car sensor
LBLOFB Left blower feedback voltage
LBLOWOP Left blower output voltage
LSERFB Lower servo feedback potentiometer
MPROBE Measurement probe
POWIN+ Switched power input
POWOP+ Power output
RBLOFB Right blower feedback voltage
RBLOWOP Right blower output voltage
REF Reference signal
REVSERL Lower servo reverse drive
REVSERU Upper servo reverse drive
TEMPDEM Temperature demand
USERFB Upper servo feedback potentiometer
WATSW Water switch
WATVAL Water valve
8-66 May 1996

^=2?
Air Conditioning
Portable Diagnostic Unit - Signal Definitions
ThefollowingsignalsaresupportedontheAir-ConditioningControlModule. For each signal. The signal name, mnemonic
and background information are detailed.
Ambient Temperature Sensor
(AMBTEMP)
Auto-Recircuiation Input
(ARECIP)
Auto-Recirculation Output
(ARECOP)
Auxiliary Battery Positive
(AUX+)
Clutch Relay Drive Output
(CLUREL)
A/CCM Pin 34 ref Pin 6
This sensor is located in the right hand blower motor. This signal is used to enable
the A/C system to compensate for changes in ambient air temperature. The output
to pin 34 is 2.732 volts at 0 degrees Celsius and changes by 0.01 volts for each
degree Celsius above or below zero.
A/CCM Pin 9 ref Pin 6
This is effectively an On/Off switch for the A/C system and forms part of the fan
control switch.
Switch Off - Pin 9 should be at ground
Switch On - Pin 9 should be at 10+ volts.
When pin 9 is at ground, pin 3 will be at 10+ volts causing the recirculation flaps
to open.
A/CCM Pin 3 ref Pin 6
This signal will cause the recirculation flaps to close. Operating conditions should

be:

A/C Off - 10+ volts at pin 3, flaps open.
Temp demand minimum - 10+ volts at pin 3, flaps open.
Defrost - 0 volts at pin 3, flaps closed.
Temp demand max - 0 volts at pin 3, flaps closed.
A/CCM Pin 1 ref Vehicle Battery -ve
This signal istheauxiliary supply to the A/CCM. Pin
1
should read battery voltage
if the ignition switch is in the auxiliary or ignition on positions. Pin
1
should read
0 volts when the ignition switch is in the Off position or in position III whilst
cranking the engine. Loss of this supply will cause total failureof the A/C system.
A/CCM Pin 20 ref Pin 6
This signal responds to the input at pin 5 (evaporator sensor). When pin 5 is
between 2.715 and 2.725 volts, pin 20 should read below 1 volt, and the
compressor clutch will be switched off. When pin 5 is between 2.735 and 2.745

volts,
pin 20 will rise to 10+ volts and the compressor will re-engage.
Centre Vent Solenoid
(CVSOL) A/CCM Pin 18 ref Pin 6
The centre vent solenoid controls the operation of the centre vent flap. The centre
vent will open to increase the cooling capabilities of the vehicle when cooling is

selected.
In all other conditions, the centre vent will be closed.
Solenoid energised: pin 18 should read 10+volts and the centre vent will be open.
Solenoid de-energised; pin 18 should read below 0.5 volts and the centre vent
should be closed.
May 1996 8-67