1997 ASTON MARTIN DB7 relay

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

^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
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
Lower Feedback Potentiomenter "3^^?
Blower Motors Potentiometers
The air conditioning system has two blower motors

(Fig.
1
-7) that operate together to maintain the flow
of air into the car at the desired
level.
The motors are
supplied from an ignition switched supply through
transistorised control circuits fitted in the motor
outlets. The circuits steplessly vary the speed of the
motors at
1
and 2 selections of the mode switch and
operate the motors to high speed when 3
is
selected.
The electronic components are assembled on a
heat sink and include a power transistor (Fig.
1
-9)
and feedback diode (Fig. 1-8). The switches are
supplied and controlled by the ECM.
When the mode switch is set to 3, the high speed
relay (Fig. 1-10) is energised from pin 16 of the

ECM,
opening
a
path to earth-ground, and allowing
full battery voltage to be applied to the motor. At 1
and 2, the motor is supplied with a continuously
variable voltage by the power transistor and the
earth-ground return is made via the ECM. The
feedback diode enables the ECM to sense the
voltage at the negative terminal of the blower
motor.
Lower Feedback Potentiometer
The lower feedback potentiometer determines the
position of the lower blend flap in the air
conditioning unit and feeds this information to the

ECM.
The ECM is thereby able to command the
lower flap servo motor to move the flap to a new
position and maintain the temperature of the air to
the feet and rear outlets at the desired level.
V 1
• 2
V3
Figure 1.
Key to Fig. 1

1.
Output signal from Pin 16 ECM

2.
Power feed
3. Blower feedback
Left hand Pin 22, Right hand 33

4.
Blower output Left Pin 31, Right 32
5. Control switch earth-ground
6. ECM earth-ground Pin 45
7. Blower motor
8. Feedback diode
9. Power transistor

10.
High speed relay
Figure 1.

1.

2.

3.
+5 volts from ECM Pin 43
Feedback signal to ECM Pin 29
Earth-Ground
The potentiometer is supplied with +5V from pin
43 of the ECM and returns its feedback signal via
pin 29. The feedback signal is 10OmV (COLD AIR)
to 1.2 V (HOT A!
R).
The potentiometer also provides
a single feedback signal of 2.9V when the blend
flap is in DEFROST. In this position, the feet and
rear outlets are closed and all air is directed to the

screen.

8-26 May 1996

"3^2?
Air Conditioning
System Fault Diagnosis
Mode Switch: Low - Function Switch: Manual
Low input 13
Clutch output- Evap sensor below 2.72V 20
Clutch output- Evap sensor above 2.72V 20
Medium input 14
High input 15
Defrost 27
From ON-OFF Switch. 44
Output 43
Recirc. output 3
HS Relays 16
Water valve solenoid 17
Centre vent solenoid 18
Mode Switch: Medium - Function Switch: Manual
Low input
Medium input
High input
Defrost
13
14
15
27
Mode Switch: High Servo Motors Stationary - Function Switch: Manual
Low input 13
Medium input 14
High input 15
Defrost input 27
Mode Switch: Defrost - Function Switch: Manual
Low input
Medium input
High input
Defrost input
13
14
15
27
Mode Switch: Low, Medium or High - Function Switch: Manual
Air Differential - cold face 28
Air Differential - hot face 28
Mode Switch: Low, Medium or High - Function Switch: Manual

Temp.
Maximum demand 35

Temp.
Minimum demand 35
150 to 350mV
0.6V
11.4V
3to5V
3to5V
3to5V
10.3 to 13.3V
4.73 to 5.2V
0 to 200mV
0 to 200mV
0 to 200mV
0 to 200 mV
3to5V
150 to 350mV
3to5V
3to5V
3to5V
3to5V
150 to 350V
3to5V
3to5V
3to5V
3to5V
150 to 350mV
2.665 to 3.105V
0 to 200mV
2.665 to 3.105V
0 to 200mV
Mode Switch: Low, Medium or High Temperature Demand Switch: Mid-Range - Function Switch: AC
Servo motor lower flap 37 0 to 2.0V
Servo motor lower flap 41 0 to 2.0V
Servo motor upper flap 40 0 to 2.0V
Servo motor upper flap 42 0 to 2.0V
Mode Switch: Low, Medium or High Temperature Demand Switch: Mid-Range - Function Switch: AC
Servo motor lower flap 37 7.0 to 9.5V
Servo motor lower flap 41 7.0 to 9.5V
Serve motor upper flap 40 7.0 to 9.5V
Servo motor upper flap 42 7.0 to 9.5V
May 1996 8-31

Air Conditioning
System Fault Diagnosis D^
Mode Switch: Low or Medium Temperature Demand Switch: Mid-Range - Function Switch: AC
10 to 12V
0 to SOOmV
2.875 to 2.895V
0 to 500mV
0 to 500mV
0.6 to 0.9V
1.15 to 1.45V
260 to 460mV
4.5 to 5.5V
0 to 500mV
10.3 to 13.3V
10 to 13V
10 to 13V
0 to 0.5V
0 to 0.5V
0 to 500mV
0 to SOOmV
Recirc. input
Recirc. output
Reference voltage
Defrost output
High speed relays
Lower feedback pot.
Upper feedback pot.
Water temp, switch engine cold
Water temp, switch engine hot
Defrost output
Clutch output- evaporator
above 2.745 V
Right hand Blower feedback
Left hand Blower feedback
Right hand Blower control
Left hand Blower control
Water valve solenoid
Centre vent solenoid
9
3
7
11
16
29
30
21
21
11
20
33
22
32
31
17
18
Mode Switch: (Auto) Low Temperature Demand Switch: Minimum
Face Level to mid-range 28 1.43 to 1.45V
Servo Motors Stopped
Servo motor lower flap 37 0 to 40mV
Servo motor lower flap 41 0 to 40mV
Servo motor upper flap 40 0 to 40mV
Servo motor upper flap 42 0 to 40mV
Lower feedback pot. 29 0 to 0.2V
Upper feedback pot. 30 0 to 0.2V
Mode Switch: Low Temperature Demand Switch: Mid-Position - Function Switch: AC
Temperature demand 35 1.43 to 1.45V
Servo Motors Stopped
Servo motor lower flap 37 0 to 40mV
Servo motor lower flap 41 0 to 40mV
Servo motor upper flap 40 0 to 40mV
Servo motor upper flap 42 0 to 40mV
Lower feedback pot. 29 0.57 to 0.87V
Upper feedback pot. 30 0.6 to 0.9V
Mode Switch: Low Temperature Demand Switch: Maximum - Function Switch: AC
Temp demand 35 2.665 to 3.105V
Lower flap feedback pot 29
Upper flap feedback pot. 30
0.979 to
1.279V

1.518 to 1.9V
Mode Switch: (Auto) Face Level: Cold Face
Differential temp. 28
Lower flap feedback pot. 29
Upper flap feedback pot. 30
2.665 to 3.105V
0.979 to
1.279V

1.340 to
1.640V

8-32 May 1996

^7?
Air Conditioning
System Fault Diagnosis
Blower Motor Test
Face Level: Hot Face Temperature Demand Switch: Minimum
Differential temp. 28 0 to 200mV
Temperature demand 35 0 to 200mV

Hote:
Allow
the servo motors
to
come to rest before checking voltage
levels.
Typical figures are given
in
brackets.

Mode Switch
Position
Low
Med
High
RH Control
Pin No. 32
1 - 2V (1.77V)
3V (2.28V)
2v
(1.1
7V)
Set Face Differential Pot. to Mid Point
Mode Switch RH Control
Position Pin No. 32
Low 1 - 2V (1.24V)
Medium 1 - 2V (1.4V)
High 2-3V(2.2V)
Set Face Differential Pot. to Cold Face
Mode Switch
Position
Low
Medium
High
RH Control
Pin No. 32
1 - 2V(1.67V)
2 - 3V(2.17)
2 - 3V(2.3V)
LH Control
Pin No. 31
1 -2V(1.77V)
2 - 3V (2.27V)
1 - 2V (1.19V)
LH Control
Pin No. 31
1 - 2V (1.27V)
1 - 2V (1.4V)
2 - 3V (2.2V)
LH Control
Pin No. 31
1 - 2V(1.63V)
2-3V(2.1V)
2 - 3V(2.2V)
RH Feedback
Pin No. 33
4 - 6V (5.8V)
3 - 5V (3.7V)
1 - 2V (1.22V)
RH Feedback
Pin No. 33
6.5 - 9V (8.7V)
6.9 - 9V (7.5V)
3-5V(4.1V)
RH Feedback
Pin No. 33
6.5 - 9V(6.25)
3 - 5V(4.25V)
3 - 5V (3.7V)
Open Water Temperature Switch Needs
Set Temperature Demand Switch to Midpoint Pin No. 35 1.43 -145V
RH Servo control Pin 32
LH Servo control Pin 31
Short Water Temperature Switch Leads
Mode Switch: Low
Clutch output
RH Servo control
LH Servo control
Set d iff to hot face
Set temp demand to minimum
Recirc. output
High speed relays
Water valve solenoid
Centre vent solenoid
Defrost output
MODE SWITCH: DEFROST
High speed relays
Lower feedback pot.
Upper feedback pot.
MODE SWITCH: OFF
Recirc. output
Pin 20
Pin 32
Pin 31
Pin 28
Pin 35
Pin 3
Pin 16
Pin 17
Pin 18
Pin 27
Pin 27
Pin 16
Pin 29
Pin 30
Pin 44
Pin 3
LH Feedback
Pin No. 22
4 - 6V (5.63V)
3 - 5V (3.4V)
1 -2V (1.27V)
LH Feedback
Pin No. 22
6.5 - 9V (8.7V)
6.5 - 9V (7.5V)
3 -5V (4.0V)
LH Feedback
Pin No. 22
6.5 - 9V(6. IV)
3 - 5V(4.2V)
3 - 5V(3.SV)
0.5V
0.5V
9.3-12.3V
1 -2V
1 -2V
0 - 200mV
0 - 200mV
9.3-12.3V
0 - 200mV
9.3-12.3V
9.3-12.3V
0 - 500mV
150-350mV
9.3-12.3V
2.709-3.1 OOV
1.714-2.014V
0-IV
9.3-12.3V
May 1996 8-33

'^T?
Air Conditioning
Compressors
Compressors
Compressor Clutch Control
The compressor
pu I
ley
is
driven continuously when
the engine is running. An electromagnetic clutch
allows the compressortobeengagedordisengaged.
The clutch is energised by battery supply voltage
when the clutch relay RF3 is closed by a signal from
the ECM (pin 21) via the engine management

system.

6^
o>o 1
4
Figure 1
Figure 2
Key to Fig. 2

1.

2.

3.

4.

5.
Condenser
Clutch relay supply
Compressor clutch
HSLP switch
Protection diode
Earth-ground
Key to Fig. 1

1.
+ve battery supply

2.
Clutch relay
3. Compressor clutch

4.
Pin 20 ECM supply to clutch relay solenoid
5. Earth-Ground
6. Earth-Ground
Trinary Switch
High Side Low Pressure Switch
The high side low pressure switch (HSLP) is
connected in the earth-ground return lead of the
compressor clutch
coil.
The switch is a function of
the trinary switch and monitors the pressure on the
high side of the refrigeration system. If the pressure
drops below 25 psi (+ 5 psi) the contacts open to de-
energise the clutch coil and disengage the clutch.
Low pressure occurs when there is a fault in the

system,
and the HSLP switch contacts remain open
until the fault has been rectified.
The condenser (Fig, 3) consists of a refrigerant coil
mounted in a series of thin cooling fins to provide
maximum heat transfer in the minimum amount of

space.
It is mounted directly behind the car radiator
and receives the fu
11
flow of ram air induced by the
forward motion of the car and the suction of the
cool ing
fan.
Refrigerant enters the inlet at the top of
the condenser as a high pressure hot vapour. As the
vapour passes down through the condenser coils
cooled by ram air, a large quantity of heat is
transferred to the outside air and the refrigerant
changes to a high pressure warm liquid.
May 1996 8-35