1997 ASTON MARTIN DB7 compressor

^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
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
In Car Controls ^2?
Evaporator Sensor
The evaporator sensor allov^^s the ECM to monitor
the temperature ofthe refrigerant in the evaporator
core continuously. When the temperature falls
below 0°C the ECM de-energises the compressor's
electromagnetic clutch and prevents refrigerant
from flowing through the system. The clutch is re­
engaged when the temperature rises.
Motorised In-Car Aspirated Sensor
The motorised aspirator (Fig. 8), which is fitted to
the passenger side facia underscuttle panel,
incorporates a motor driven fan (Fig. 8-1) that
draws air continuously over the in car temperature
sensor (Fig. 8-2).
Figure 8.
Key

1.

2.

3.

4.

5.
to Fig. 8
Motor
Sensor
Fan
Connector SCAO07
Connector SAC030
The motor (Fig. 8-1) is supplied, independently of
the air conditioning
system,
from the ign ition switch
(position 2). Its operating voltage range is 13.5 to
14.2 volts. Maximum current is 120 mA. The sensor

(Fig.
8-2) has a temperature operating range of -
30°C to +85°C. It is fed with 5 volts from the ECM
(pin 43), while the sensing voltage
is
supplied to pin
4 ofthe ECM. At 0°C the sensing voltage is 2.732V
± 0.002V. The rate of change of sensing voltage is
0.01 V± 0.002V per 1°C.
LC/0
0^5
U
Figure 9.
Key to Fig. 9

1.
Ignition switched supply to motor

2.
+5V supply to sensor from pin 43 of ECM
3. Sensor voltage output to pin 10 of ECM

4.
Sensor earth-ground to pin 4 of ECM
5. Motor earth-ground
A. Motor
B. Sensor
Ambient Temperature Sensor
An ambient temperature sensor (Fig. 10-1) is fitted
in the plenum air intake to provide the ECM with
information on the temperature ofthe air entering
the air conditioning unit and so offset the in-car
temperature at extremes of ambient. The voltage
signal output from the sensor is proportional to the
temperature of the surrounding air. The sensor
temperature range is -30°C to 85°C. At 0°C the
output ofthe sensor is 2.732V ± 0.005V. The rate
of change is + 0.01 V ± 0.002V per
1
°C.
Figure 10.
Key to Fig. 10

1.
Ambient temperature sensor

2.
+5 volts from ECM Pin 43
3. Sensing signal to ECM Pin 34

4.
Earth-ground
8-24 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
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

Air Conditioning
Compressors ^?
Evaporator
Figure 3.
Receiver-Drier
The receiver drier (Fig. 1) accepts high pressure
warm refrigerant liquid from the condenser and
del ivers it via an expansion valve to the evaporator.
It contains a quantity of molecular sieve desiccant
to remove moisture from the refrigerant, and
a
fi Iter
to removecontaminants.lt also
a
providesa reservoir
of refrigerant for the evaporator under varying
operating conditions.
The evaporator consists of a refrigerant coil mounted
in a series of thin fins to provide a maximum
amount of heat transfer in a minimum amount of

space.
It is housed in the air conditioning unit and
all air entering the system passes across its
coil.

The evaporator receives refrigerant from the
thermostatic expansion valve as a low pressure
cold atomised liquid. As this cold liquid passes
through the evaporator coils, it absorbs heat from
the surrounding air and changes into
a
low pressure
warm vapour.
Expansion Valve
The expansion valve is the dividing point between
the high and low pressure sides of the system. It
automatically meters high pressure, warm liquid
refrigerant via a metering orifice into the low
pressure, cold side of the evaporator matrix. The
valve senses outlet pipe temperature, inlet pipe
pressure and regulates the flow of refrigerant into
the evaporator to ensure that only vaporised
refrigerant appears at the outlet.
Figure 1.
8-36 May 1996

^?
Air Conditioning
Sanden Compressor SD7H15
Sanden Compressor SD7H15
The Sanden SD7H15 compressor
is a 7
cylinder
machine with
a
bore
of
29.3
mm (1.15 in) and a

stroke
of
32.8
mm (1.29
inches).
The displacement
per
revolution
is
155cc
(9.5

cubic inches).
The magnetic clutch
is
engineered with
the

compressor
as a
complete assembly resulting
in a

relatively small unit
of
lightweight construction.
The compressor may be mounted up to 90° from
its

upright position.
The compressor incorporates
a
lubrication system
which reduces the
oil
circulation ratio
to a
level
of

less than
2% at 1800 rpm.

An
oil
deflector
and
positive pressure differential
lubrication system promotes oiling
to the
cylinder

wall,
piston
rod
assemblies, main bearings
and

shaft
seal,
and
ensures that
oil
circulation
to the

refrigeration circuit
is
kept
to a
minimum.
The

compressor ischarged
with!
35 cc(4.6fluid ounces)
ofSunico NoSGSoil at the factory. Only this oil
or

oneoftheequivalentoilsdetailed below should
be

used.

Key

1.

2.

3.
4.
5.
6.
7.
8.

9.
10.

11.

12.
13.
14.
15.
16.

to Fig. 2.
Service port
Cylinder head
Hose connection
Anti-rotation gear
Oil filler plug
Planet plate
Clutch bearing
Electromagnetic clutch
Valve plate assembly
Cylinder and valve plate gasket
Cylinder block
Piston
Cam rotor
Needle thrust bearing
Front housing and 'O' ring
Shaft seal
Compressor Oils
Suni
CO
No 5GS
Texaco Capella E
Virginia Chemicals 500 Viscosity

13
14 15 16

Figure
2.

May
1996
8-37