1997 ASTON MARTIN DB7 ESP

Air Conditioning
Temperature Distribution System
The Control Panel (Fig. 4) contains:
• Fan speed-defrost rotary switch (Mode-Switch),
• Air Conditioning Function Switch
• Temperature differential rotary control
• Temperature rotary control,
The control panel relays information to the ECM.
Figure 4.
Fan Speed Control (Mode Switch)
The rotary switch controls airflow from the blower motors. The switch has five positions: 3C, 1, 2,3 and DEFROST.
«» The system is not operational; a residual signal is sent to the Electronic Control Module (ECM)
to ensure that the blower flaps are closed to prevent outside air from entering the system.

1,
2,3 Selection information is relayed to the ECM. Signals are also relayed to the ECM from the
temperature selector feedback circuits and various sensors. Fan speed is steplessly controlled
by the ECM, within the ranges 1, 2 and 3.
DEFROST the fans operate at maximum speed, front screen vents open fully, lower flaps close fully and
maximum output is directed to the windscreen (there may be a delay of up to 30 seconds from
selection to execution of this function).
Face Level Temperature Differential
This control is used to vary the temperature difference between the air coming through the face vents and that coming
through the lower vents into the footwell.
Temperature Rotary Control
This is used to preset the in car heat level in either automatic or manual mode. There are three temperature sensors
located in the system:
• Exterior ambient
• In-car
• Evaporator.
An input voltage is supplied to the sensors from AC4-13 of the control module. The temperature sensing signal from
the sensors is transmitted to the control module via AC4-4 and AC2-4 respectively. The sensors are semiconductor
devices which provide a voltage output proportional to the sensed temperature.
8-10 May 1996

Air Conditioning
In Car Controls '^^
Air Conditioning Function Switch
The air conditioning function switch (Fig. 4) has
five positions: Economy (ECO), Air conditioning

(AC),
Manual (MAN), Re-circulation and Demist
(DEM). These settings have thefol lowing functions:
ECO (Economy) Inthissettingtheairconditioning
compressor is switched off. No cooling is
available but incoming air may be heated to
the selected temperature. This mode puts a
minimum load on the engine. Pin 23 at the
ECM is earthed through the switch to select
economy mode.
AC This setting allows the heating and cooling
functions to be performed automatically,
the required in-cartemperature
is
maintained
and the air is dehumidified. Pin 26 at the
ECM is earthed through the switch to select
this mode.
MAN (Manual) In the Manual mode the fan speed
and temperature control can be set at any
level and heating or cooling will be
performed despite the internal temperature
of the car. Pins 26 and 19 at the ECM are
earthed through the switch to select this
mode
V (Re-circulation) With this setting selected
the external air inlets are closed and
conditions are maintained by circulating
the air within the car. Heating and cooling
functions are controlled automatically to
give the required in-cartemperature. Pins 9
and 26 at the ECM are earthed through the
switch to select the manual Re-circulation.
DEM (Demist) Air is directed directly onto the
screen in this mode. Air speed and
temperature depend on the selected fan
screen and in-cartemperature. Heating and
cooling functions are still controlled
automatically to give the required in-car
temperature. Pin 8 and 26 at the ECM are
earthed through the switch to give the
required in-car temperature.

B
liD^
-• 1
-• 2
-• 3
-• 4
-• 5
,'^
1 -• 6
-• 7
-• 8
Figure 4.
Key to Fig. 4

1.
AC signal Pin 26 ECM

2.
MAN signal Pin 19 ECM
3. REC signal Pin 9 ECM

4.
DEM signal Pin 8 ECM
5. Earth-ground Pin 1 ECM
6. Earth-ground Pin 1 ECM
7. AC signal Pin 26 ECM
8. ECO signal Pin 23 ECM
A ECO
B AC
C MAN
D Re-circulation
E DEM
8-22 May 1996

Air Conditioning
Vacuum System •^^
Vacuum System The flaps in the cabin air distribution vents and the
water valve in the pipeline from the engine coolant
system to the heater matrix are all operated by
vacuum actuators. The vacuum forthese
is
supplied
by four solenoids mounted in pairs behind the front
footwell outlets. Each solenoid and its associated
pipe work is identified by a colour:
Defrost
Auto Re-circulation
Water valve
Centre vent
Green
Blue
Red
Black.
The vacuum supply pipes to the re-circulation and
centre vent actuators are fitted with restrictors in
order to slow down the operation of the flaps and
avoid hunting. The re-circulation flaps can take up
to 30 seconds to move to a new position.
Vacuum is piped to the solenoids from the engine
manifold through a reservoir. The solenoids are
energised by signals from the ECM in response to
demand ,sensing and feedback signals.
-T^^^T 2
3
figure 7.
Key

1.

2.

3.

4.

5.
6.
7.
8.
9.

10.

11.

12.

13.

14.

to Fig. 1
Vacuum reservoir
Defrost solenoid
Defrost-demist actuator
Restrictors
Centre vent solenoid
Centre vent actuator
Defrost vacuum pipe
Centre vent vacuum pipe
Recirc. solenoid
Recirc actuator
Recirc. vacuum pipe
Water valve solenoid
Water valve actuator
Water valve vacuum pipe
Figure 2.
5
7
10
Key to Fig. 2

1.
Defrost (Green) solenoid

2.
+12V Defrost Input from ECM pin 12
3. Defrost output to ECM Pin 11

4.
Recirc (Blue) solenoid
5. +12V Recirc. input from ECM Pin 3
6. Water valve (Red) solenoid
7. +12V Water valve input from ECM Pin
1
7
8. Centre vent (Black) solenoid.
9. +12V Centre vent input from ECM Pin 18

10.
ECM earth-ground
8-28 May 1996

Air Conditioning
System Checking with the Manifold Gauge Set [n::S3^^?
Refrigerant Excessively Low.
Complaint.
Cooling is not adequate.
Air In The System.
Complaint.
Cooling is not adequate.
BLU£ LOW SIDE SlUE LOW SIDE MD HIGH SIDE
5.
6.
7.

Condition.

1.
The low side gauge is reading very low.

2.
The high side gauge reading very low.
3. No bubbles or liquid evident in the sight glass.

4.
The discharge air from the evaporator is warm.
Diagnosis.
System refrigerant excessively low. Serious leak

indicated.

Correction.

1.
Test the system for leaks.
Note: Partially recharge the
system
before testing the

system
for
leaks
to
ensure that leak detection is
obtained.
Depressurise the system.
Repair the leaks, and if necessary renew hoses or

units.

Check the compressor oil level. The system may
have lost oil due to leakage.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
performance.

2.

3.

5.
6.
7.
8-42
Condition.
The low side gauge reading
is
constant and does not

drop.
The pressure should drop until the compressor
cycles (thermostat control)
The high side gauge reading is slightly high (or
slightly lower especially if a large fan is used to
substitute ram air).
The sight glass is free of bubbles or only shows an
occasional bubble.
Thedischarge air from theevaporator
is
only slightly

cool.

Diagnosis.
Non condensables present in the system. Air or
moisturepresent instead of afullrefrigerantcharge.
Correction.
Test the system for leaks. Test the compressor seal
area very carefully.
Depressurise the system. Repair the leaks, and if
necessary renew hoses or units.
Renew the drier bottle, probably water saturated .
Check the compressor oil level.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
Operate the system and check the performance.
May 1996

Air Conditioning
Air-Conditioning Diagnostics
The Air Conditioning System Diagnostics
The air-conditioning control module (A/CCM) is located at the right end of the air-conditioning unit.

A
digital microprocessor within the
A/CCM
receives
data
signals from
the
operator controlled
switches.
Comparison
of these signals with those returned from the system temperature sensor and feedback devices results in the
appropriate voltage changes necessary to vary: blower motor
speed,
flap positions and system solenoids to respond
to the drivers selected temperature demand.
The air from the two blower motors is passed through the evaporator matrix which, depending on the A/C mode

selected,
removes heat from the incoming air. Depending on the position of
the
two blend
flaps,
the cold air passes
either directly into the vehicle outlet vents, or is passed through the heater matrix to be reheated and then passed
to the vehicle outlet vents.
The amount of air passing through the heater matrix is infinitely variable depending on ambient temperature and
the temperature selected within the vehicle.
Air Conditioning Diagnostics
Cable Connections to the A/CCM
Cable Setup
Figure 1. PDU connections to the A/CCM

1.
Remove the right side underdash trim panel.

2.
Connect the VBA (0024) to the vehicle battery
3. Connect the PDU to the VBA (0024).

4.
Connect the VIA to the PDU using the VIA-PDU cable (0030).
5. Connect the AirCon Datalogger harness (0780) between the VIA Channel A and the Air-Conditioning Control
Module on the vehicle.
May 1996 8-65

^=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

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/CCMPin2refPin6
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

The Aston Martin Lagonda Diagnostic System
Installation Instructions E:MB^^?
Introduction The Aston Martin Diagnostic System
This guide contains instructions for the installation
of the Portable Diagnostic Unit hardware in Aston
Martin Dealer workshops. To achieve maxinnum
benefit from the system, please follow the
instructions carefully. The following System
Diagram shows the principal system components
and panel details.
This introduction briefly describes the system and
its capabilities. This is followed by the Installation
and Power-Up procedures which give detailed
instruaions on how to start the system and access
the self-contained Interactive
Training
Programme.
The subsequent sections detail the fault diagnosis
and maintenance procedures.
WARNING:
The equipment must
only
be used by

trained
personnel.
Care should
be taken to use the

equipment in accordance with the operating

procedures.
Observe
all safety
warnings
in this

guide.
If any part of
the system is damaged do not

use it. Call your local CenRad
Service
Centre

immediately
for a
substitute
part.
Refer to
'Parts

Ordering'.
The Aston Martin Diagnostic System is a new
generation diagnostic
tool
which fulfils
a
number of
functions in aiding the technician to quickly and
accurately locate faults. The heart of the system is
the Portable Diagnostic
Unit,
a
lightweight powerful
computer/measurement system providing a step-
by-step user friendly interface for the technician.
PDU functions include:
Data Logger - The ability to monitor and record
control module signals even whilst the vehicle is
being driven.
On-Line Help-Containing detailed descriptions in
the
operation
ofthevehicleselectroniccomponents.
Vehicle Setup - The ability to setup various
adjustable parameters to their optimum settings.
Diagnostic Trouble Codes - The ability to extract
recorded fault information from the DB7's control
modules.
Each of
these
funaions is described in detail in the
PDU Users Guide.
WARNING: If
the system is used to measure high

voltages,
these voltages can appear on the pins of

other
connectors in
the
system.
Ensure
that socket
covers
are
fitted
on
unused
sockets.
Ensure
that all

connections
are
made
prior to
applying the high
voltage to
the
probes.
Do not
leave the equipment
unattended
in
this
state.
The maximum
voltage

that may be applied
between the
test
probes is 150
volts
AC or DC.
Radio Interference Statements
This digital apparatus does not exceed the Class A
limits for radio noiseemissionsfromdigital apparatus

as set
out
in
the radio interference regulations of the
Canadian Department of Communications.
This equipment has been tested and found to
comply with the limits for Class A digital device
pursuant to part 15 of the Federal Communications
Commission (FCC) rules. However, operation in
close proximity to domestic communication
equipment may cause interference. It is the
responsibility of the user to avoid or correct this

condition.

9-2 May 1996