1997 ASTON MARTIN DB7 Workshop Manual

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
Pressure-Temperature Graphs
Pressure-Temperature Graphs
To obtain Bar multiply the Ibf/in
^
by 0.068
To obtain kgf/cm^ multiply
Ibf/in^
by 0.07
High Side (Ibf/in^) - Ambient (°C)
350
i 250
200
150
•inn
15 18 21 24 27 30 32 35 38 40 43 46 49
C
Low Side (Ibf/in^) - Ambient (°C)
80
70
60
CM C
~ 50
n
40
30
20
10
May 1996 8-29

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

"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

Air Conditioning
Refrigeration /s:s^°27
Refrigeration
Safety Precautions
The air conditioning system is designed to use only
Refrigerant E134A (dichlorodifluoromethane). Extreme
care must betaken NOT to use
a
methylchloride refrigerant.
The chemical reaction between methylchloride and the
aluminium parts ofthe compressor results in the formation
ofproductswhich burn spontaneously on exposure toair,
or decompose with violence in the presence of moisture.
The suitable refrigerant is supplied under the following
names.
El 34A KLEA or equivalent
Warning: Take care when handling refrigerant. Serious
damage will occur if it is allowed to come into
contact with the eyes. Always wear with goggles
and gloves when working with refrigerant
First Aid
If refrigerant should come into contact with the
eyes or
skin,
splash the eyes or affected area with
cold water for several minutes. DO NOT RUB. As
soon as possible thereafter, obtain treatment from a
Doctor or an eye specialist.
Good Practice

1.
Protective sealing plugs must be fitted to all
disconnected pipes and units.

2.
Theprotectivesealingpiugsmustremain inposition
on ail replacement components and pipes until
immediately before assembly.
3. Any part arriving for assembly without sealing
plugs in position must be returned to the supplier as
defective.

4.
It is essential that a second backing spanner is
always used when tightening or loosening all joints.
This minimises distortion or strain on components
or connecting hoses.
5. Components must not be lifted by connecting

pipes,
hoses or capillary tubes.
6. Care must be taken not to damage fins on the
condenser or evaporator matrices. Any damage
must be rectified by the use of fin combs.
7. Before assembly oftube and hosejoints, use
a
small
amount of clean new refrigerant oil on the sealing
seat.
8. Refrigerant oil for any purpose must be kept very
clean and capped at all times. This prevents the oil
absorbing moisture.
9. Before assembly the condition of joints and flares
must be examined. Dirt and even minor damage
will cause leaks at the high pressure points
encountered in the system.

10.
Dirty end fitting can only be cleaned using a cloth
wetted with alcohol.

11.
Afterremovingsealingplugsand immediatelybefore
assembly, visually check the bore of pipes and
components. Where any dirt or moisture is

discovered,
the part must be rejected.
12. Ail components must be allowed to reach room
temperature before sealing plugs are removed.
This prevents condensation should the component
be cold initially.

13.
Before finally tightening hose connections ensure
that the hose lies in the correct position, is not
kinked or twisted and will not be trapped by
subsequent operations, e.g., refitting or closing
bonnet.

14.
Check that hoses are correctly fitted in clips or
straps.

15.
The compressor must be stored horizontally with
the sump down. It must not be rotated before fitting
and charging. Do not remove the shipping plate
until immediately before assembly. Always use
new "O" ring seals in those joints that incorporate

them.
"O" ring seals should be coated with
compressor oil before fitting.

16.
Components or hoses removed must be sealed
immediately after removal.
1 7. Afterthe system has been opened the receiver-drier
must be renewed.

18.
Before
testing,
run the engine until normal running
temperature is reached. This ensures that sufficient
vacuum is available for test. For cooling tests the
engine must be running for the compressor clutch
to operate.
8-34 May 1996

'^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