1997 ASTON MARTIN DB7 coolant

^2?
Air Conditioning
Electronic Control Module
Electronic Control Module (ECM)
The Electronic Control Module (ECM) is located on the right hand side of the heater unit.
The ECM has a digital microprocessor that allows the air conditioning system to maintain the selected in-car
conditions. To do this it compares the signals from the in-car controls with those it receives from the system
temperature sensors and feedback
devices.
On the basis of these comparisons it makes appropriate voltage changes
to vary the blower motor
speed,
flap position and the state of other solenoids that effect the selected temperature

demand.

The ECM is a non-serviceable component but may be interrogated for system
testing.
Care must be exercised when
connecting
the test
equipment
as the ECM
may
be
irreparably
damaged
should any ofthe
test
pins
be
shorted or bent.
20 21 22 23
Q
A / A \/
Em
10 11

1.
Electronic control module (ECM)

2.
Differential temperature control
3. Temperature control

4.
Fan speed control
5. Ambient temperature sensor
6. Motorised in-car aspirator
7. Evaporator temperature sensor
8. Coolant temperature switch
9. Lower flap feedback potentiometer

10.
Upper flap feed back potentiometer

11.
Left hand blower motor feedback

12.
Right hand blower motor feedback

13.
High speed relay

14.
High speed relay

15.
Compressor clutch

16.
Blower motor

17.
Blower motor

18.
Lower flap servo motor

19.
LIpper flap servo motor

20.
Defrost vacuum solenoid

21.
Auto re-circulation vacuum solenoid

22.
Centre vent vacuum solenoid

23.
Water valve vacuum solenoid

24.
Air conditioning function switch
May 1996 8-19

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

^2?
Air Conditioning
System Checking with the Manifold Gauge Set
Compressor Malfunction
Complaint.
Cooling is not adequate.
Condenser Malfunction or System Overcharge
Complaint.
Little or no cooling. Overheating of the engine may
also be noted.
BLUE LOW SIDE

BLUE
LOW SIDE BED HICH SIDE
Condition

1.
The low side gauge reading is too
high.

2.
The high gauge reading is too low.
3. The sight glass is free of bubbles and the system is
fully charged.

4.
The discharge air from the evaporator is not
sufficiently
cool.

Diagnosis.
Internal leak in the compressor.
Correction.

1.
Depressurise the system.

2.
Renew the compressor and the drier bottle.
3. Evacuate the system using a vacuum pump.

4.
Charge the system with new refrigerant.
5. Operate the system and check the performance.
HIGH
Condition.

1.
The low side gauge reading excessively
high.

2.
The high side gauge reading is also excessively

high.

3. Bubbles may appear occasionally in the sight glass
and the liquid line to the evaporator is very hot.

4.
The discharge air from the evaporator is warm.
Diagnosis.
The condenser not operating correctly through lack
of cooling caused by too high a high side pressure.
The system may have either
a
normal or overcharge
of refrigerant.
Correction.

1.
Checkthecompressordrivebeltforcorrecttension.

2.
Check the condenser for clogged air passages
preventing air flow through the condenser.
3. Inspect the condenser mounting for correct radiator
clearance.

4.
Check for correct fan operation.
5. Check the coolant pressure capfor correct type and

operation.

May 1996 8-43

^2?
Air Conditioning Repair Procedures
Hose - Compressor to Evaporator/Air-Con Unit Renew
8.1.06.1 Hose-Compressor
to
Evaporator
Renewal
Procedure

1.
Open the bonnet and fit a wing cover.

2.
Depressurise the air conditioning systenn.
3. Remove the hose to evaporator valve clamping

plate,
disconnect the hose from the valve, remove
and discard the 'O' ring
seal.

4.
Fit a blanking plug to the evaporator valve. Release
the evaporator hose securing clips.
5. Remove the compressor outlet port retaining bolt.
6. Disconnect the hose from the compressor, discard
the hose complete with 'O' ring seals.
7. Connect the hose to the evaporator valve and
tighten clamp onto the hose.
8. Route the hose to the compressor, fit a new 'O' ring
seal and connect it to the compressor.
9. Position the outlet port retaining plate on the
compressor, fit and tighten the securing bolt.

10.
Refit the hose to the clips.

11.
Charge the air conditioning system.

12.
Remove the wing cover and close the bonnet.
8.2.01.1 Air Conditioning Unit Renewal

1.
Disconnect the battery earth
lead.

2.
Drain the engine coolant into a suitable container.
3. Depressurise the air conditioning system.

4.
Disconnect the high and low pressure hoses and
expansion valve from the air conditioning unit (see
expansion valve renewal).
5. Slacken the coolant hose to the heater matrix pipe
securing clips and disconnect the hoses from the
matrix. (This will require the removal of the air
intake hose for access.)
6. Remove the following items from inside the car:
front seats
underscuttle panels/knee bolsters
glove box assembly
facia trim (walnut trim)
radio and ashtray
centre console switch panel assembly
instrument panel and surround trim
steering wheel and column
facia assembly complete
hoses - distribution box to door vents
facia support frame
Details and drawings of the above operations can
be found in the electrical and trim sections.
Disconnect the vacuum hoses from the blower
motors, water valve and reservoir.
Un-clip the electrical harness from the air
conditioningunit, release theelectrical connections
and reposition the harness to allow removal of the
unit.
Displace and remove the footwell ventilator ducts
and hoses (Fig. 1-1).
May 1996 8-55

Air Conditioning Repair Procedures
Air-Conditioning Unit Renew ^^?

10.
Disconnect the pliable trunking from the unit (Fig.
8.2.02.1
EvaporatOr Unit Renewal
1-2). ^

1.
Remove the air conditioning unit assembly.

2.
Remove the heater pipe guide plate securing screws
and remove the guide plate.
3. Remove the screws secu ri ng evaporator sensor and
withdraw the sensor from the evaporator.

4.
Remove the screws securing the solenoid mounting
plate and displace the mounting plates from the
unit.
5. Removetheharnesstocasingearthboltand displace
the harness.
6. Cut and remove the harness to casing securing
ratchet straps and displace the harness from the

casing.

7. Displace the vacuum hose from the casing.
8. Displace and remove the casing securing clips.
9. Splitthecasingandremovetheevaporatorfromthe
unit.

10.
Remove the expansion valve guide securing screws
and remove the plate.

11.
Displace and remove the plate from the evaporator.

12.
Fitting the new evaporator is the reversal of the
removal procedure.

13.
Refill the engine cooling system with coolant.

14.
Recharge the air conditioning system.
Figure 1

11.
Twistandpulloutthefourairconditioningunitstub
pipes (Fig. 1-3)

12.
Remove the screws securing the air conditioning
unit support stays.

13.
Displace the tunnel carpet for access to the lower
fixing bolts and remove the stays.

14.
Disconnect the condensate drain tubes.

15.
Peel off the tape securing the windscreen demist
duct to the distribution box (Fig.
1
-4).

16.
Remove the air conditioning unit to bulkhead
securing nuts.

1
7. Carefully lift out the air conditioning unit complete
with the distribution box.

18.
Remove the distribution box securing screws and
remove the assembly (Fig.
1
-5).

19.
Reverse the removal procedure to refit the air
conditioning unit.

Note:
Ensure new'O'rings
are
fitted toall air conditioning
tiose connections.
8-56 May 1996

Air Conditioning Repair Procedures
Water Temperature Switch/Heater Matrix Renew •=2?
8.2.12.1 Water Temperature Switch
Renewal

1.
Disconnect the battery earth
lead.

2.
Un-clip and remove the left hand underscuttle

casing.

Figure.
3. Note and disconnect the feed wires from the switch

(Fig.
1-1).

4.
Displace and remove the switch from the water

pipe.

5. Fitting a new switch is the reversal of the removal
procedure.
8.2.13.1 Heater Matrix Renewal

1.
Disconnect the battery earth
lead.

2.
Remove the left hand underscuttle panel.
3. (On right hand cars) Remove the glove box
assembly.
3. (On left hand cars) Remove the instrument pack
and surround
trim,
steering column and mounting
bracket.

4.
Drain the coolant into a suitable container.
5. Remove the matrix cover panel securing screws.
6. Removethe rear
panel,
displacethefront panel and
foam seal for access.
7. Place rag in position.
8. Remove screws securing the feed pipe and
disconnect the pipe from the matrix.
9. Remove and discard the gasket.

10.
Remove the screws securing the feed pipe and
disconnect the pipe from the matrix.

11.
Remove and discard the gasket.

12.
Disconnectthewatertemperatureswitchfeedwires.

13.
Remove the foam pad from the pipes.

14.
Remove the front panel from the unit.

15.
Undo the heater hose matrix pipe hose clips and
disconnect the hoses from the pipes.

16.
Reposition the pipes from the matrix.

1
7. Remove the matrix from the air conditioning unit.

18.
Fitting a new matrix is the reversal of the removal
procedure.

19.
Ensure that new gaskets are fitted.
8-62 May 1996

^>
Air Conditioning Repair Procedures
Electronic Control Module/Vacuum Solenoid Renewal
8.2.14.1 Electronic Control Module
Renew
8.3.01.1 Vacuum System Solenoid
Renewal

1.
Disconnect the battery earth
lead.

2.
Remove the right hand underscuttle casing.
3. (On left hand cars) Removethe glove box assembly.
3. (On right hand cars) Remove the instrument pack
and surround
trim.

4.
Disconnect the earth wire and three block
connectors from the control module (Fig.
1
-2).
5. Remove the securing screws and module from the
air conditioning unit (Fig. 1-1).
Fitting a new module
is
the reversal of the removal
procedure.
The flaps in the cabin air distribution vents and the
water valve in the pipe line from the engine coolant
system to the heater matrix are all operated by
vacuumactuators.The vacuumfor these issupplied
by four solenoids mounted in a manifold pack
located behind the front left hand footwell outlet.
Failureof a solenoid will require replacement of the
manifold pack.
Procedure

1.
Disconnect the battery earth
lead.

2.
Remove the following:
• glove box and lid
• facia trim (walnut strip)
• radio and ashtray
• centre console switch assembly
• left hand underscuttle casing/knee bolster
Detai
Is
ofthe above operations can be found in the
trim and the electrical sections.

2.
Remove thefixings joining the centre console to the

facia.
This allows the front of the console to be
repositioned for access.
3. Disconnect the ducting from the left hand footwell
outlet.

4.
Remove the two plastic fixings that secure the
slotted footwel
I
outlet and
si
ide the outlet out ofthe
unit.
7. Cut the tie strap holding the vacuum lines and
electrical harness to the underside of the air
conditioning unit.
8. Remove the screws that secure the manifold pack
to the underside of the air conditioning unit and
slide out the plate complete with the manifold
pack.

10.
To fit a new manifold pack reverse the steps for the

removal.

May 1996 8-63

O" D'^?
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 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/CCM Pin 30 ref Pin 6
The feedback signal informs the control module ofthe exact position of the flaps,
enabling accurate control ofthe 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 will close inhibiting the heating effort ofthe
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