compressor ASTON MARTIN DB7 1997 User Guide

^7
Air Conditioning
Temperature Distribution System
Air Conditioning Function Switch
When AC, DEM or Re-circulation ^v is selected the system engages the Air conditioning compressor using the
electromagnetic clutch. The in-car temperature is automatically corrected to the pre selected level by the system
sensors.
When MAN (manual mode) is selected it provides the operator selection of fan speed and in-car temperature
selection facilities. The in-car temperature is not thermostatically corrected to a predetermined level by the system
sensors.
When ECO is selected the system is in economy mode which allows the fan speed and heating levels to be selected
but gives no cooling. The air conditioning compressor is not engaged putting a minimum load on the engine.
When manual re-circulation is selected the blower flaps are closed and only that air which is in the vehicle is re­

circulated.
When the ignition is turned off the blower flaps revert to the fresh air position.
Refrigeration Cycle
The Compressor draws low pressure refrigerant from the evaporator and by compression, raises refrigerant
temperature and pressure. High pressure, hot vaporised refrigerant enters the Condenser where it is cooled by the
flow of ambient air. A change of state occurs as the refrigerant cools in the condenser and it becomes a reduced
temperature high pressure liquid.
Figure 5.

1.

2.

3.
Compressor
Condenser
Receiver-Drier

4.
Expansion Valve
5. Evaporator
6. Triple Pressure Switch (Trinary switch)
May 1996 8-11

Air Conditioning //~-->> ^/zz:^^ • ^ ^
General Svstem Procedures ' —"^ ^ '^ General System Procedures
From the condenser the liquid passes into the Receiver-Drier which has three functions:
• Storage vessel for varying system refrigerant demands.
• Filter to remove system contaminants.
• Moisture removal via the desiccant.
With the passage through the receiver-drier completed the, still high pressure liquid refrigerant, enters the Expansion
Valve where it is metered through a controlled orifice which has the effect of reducing the pressure and temperature.
The refrigerant, now in a cold atomised state, flows into the Evaporator and cools the air which is passing through
the matrix.
As heat is absorbed by the refrigerant it once again changes state, into a vapour, and returns to the compressor for
the cycle to be repeated (Fig. 5).
There is an automatic safety valve incorporated in the compressor which operates should the system pressure be
in excess of
41
bar. The valve re-seats when the pressure drops below 35 bar.
Note: The division of HIGH and LOW side is simply the
system pressure
differential created by the
compressor
discharge

(pressure),
suction
(inlet)
ports and
the
relative inlet and outlet
ports
of the
expansion
valve.
This
differential is critical to
system

fault
diagnosis
and efficiency checks.
System Protection
The trinary pressure switch, located in the liquid line, cuts electrical power to the compressor clutch if the system
pressure is outside of the range of 2 Bar
(1
st Function) to 27 Bar (2nd Function). The third function is to switch on
the cooling fans when pressure exceeds 20 bar.
General System Procedures
Leak Test
Faults associated with low refrigerant charge weight and low pressure may be caused by leakage. Leaks traced to
mechanical connections may be caused by torque relaxation or joint face contamination. Evidence of oil around
such areas is an indicator of leakage. When checking for non visible leaks use only a dedicated Refrigerant El 34A
electronic analyser and apply the probe all round the joint connection. Should a leak be traced to a joint, check that
the fixing is secured to the correct tightening torque before any other action is taken.
Do not forget to check the compressor shaft seal and evaporator.
Note: Never
use
a dedicated
CFC 12
or
naiced
flame type
analyser.

Charge Recovery (System Depressurisation)
The process of refrigerant recovery depends on the basic characteristics of your chosen recovery-recycle-recharge
equipment, therefore, follow the manufacturers instructions carefully. Remember that compressor oil may be drawn
out of the system by this process, take note of the quantity recovered so that it may be replaced.
CAUTION: Observe all relevant safety requirements.
• Do not vent refrigerant directly to atmosphere and always use approved recovery-recycle-recharge
equipment.
• Wear suitable eye and skin protection.
• Do not mix the refrigerant with CFC 12.
• Take note of the amount of recovered refrigerant, it indica
tes the
state of the
system
and
thus the
magnitude
of any problem.
8-12 May 1996

^2?
Air Conditioning
General System Procedures
Evacuating the System
This process, the removal of unwanted air and moisture, is critical to the correct operation of the air conditioning

system.
The procedures depends on the characteristics of the recovery-recycle-recharge equipment and must be
carried out exactly in accordance with the manufacturers instructions.
Moisture can be highly destructive and may cause internal blockages due to freezing, but more importantly, water
suspended in the PAG oil will damage the compressor. Once the system has been opened for repairs, or the
refrigerant charge recovered, all traces oi moisture must be removed before recharging with new or recycled
refrigerant.
Adding Compressor Lubricating Oil
Oil can be added by three methods, two of which are direct into the system
• via the recovery-recycle-recharge station
• by proprietary oil injector.
Equipment manufacturer's instructions must be adhered to when using direct oil introduction.
The third method may be required because of rectification work to the existing compressor, or the need to fit a new
compressor. From an existing compressor, drain the oil into a measuring cylinder and record the amount. Flush the
unit out with fresh PAG oil and drain thoroughly. Refill the compressor with the same amount of PAG oil that was
drained out originally and plug all orifices immediately ready for refitting to the vehicle. The transit lubricating oil
must be drained and discarded from a new compressor before it may be fitted. An adjustment should be made to
the system oil level by taking into account:
• the quantity found in the original compressor
• the quantity deposited in the recovery equipment oil separator from the charge recovery operation.
Typically, 80 ml can be drained from the original compressor and 30 ml found in the oil separator; the sum of these
volumes (80 + 30 = 110 ml) is the amount of fresh PAG oil that must be put into the new compressor prior to fitting.
Hote:
The
discrepancy
between
this
figure
and
the
nominal capacity of
135
ml is
caused
by normally not
recoverable
oil being
trapped in
components
such
as
the receiver-drier or
evaporator.

The above statements are only true if there is no evidence of a leak. Where a leak has been detected and rectified,
the compressor must be refilled with the specified quantity.
Caution: Always decant
fresh
oil from a sealed container and do not leave oil exposed to the
atmosphere.
PAG oil is very
hygroscopic
(absorbs
water) and rapidly
attracts
atmospheric moisture.
PAG oil must
NEVER
be mixed with mineral
based
oils.
Do not
reuse
oil following a recovery cycle,
dispose
of it
safely.

Depending on the state of the air conditioning system immediately prior to charge recovery and the rate of recovery,
an amount of oil is drawn out with the refrigerant. The quantity is approximately 30 to 40 mi; this may vary, and
the figure is given only for guidance. It is most important that the oil separator vessel in the recovery equipment is
clean and empty at the start of the process so that the amount drawn out may be accurately measured.
May 1996 8-13

Air Conditioning //—->> "^^Izz^^ • ^ ^
General System Procedures L ^—/ ' —^ ^./^
Adding Refrigerant
In order that the air conditioning system may operate efficiently it must contain a full refrigerant charge. The
indications of some system defects, and the results of certain tests, shows that
a
low charge
is
the most probable cause
of the fault. In such cases the charge shou
Id
be recovered from the
system,
the weight noted, and the correct amount

installed.

Note: Never attempt to
guess the
amount of refrigerant in
a
system.
Always recover and
recharge
with
the
correct
charge
weight,
this is the only
accurate
method.
Caution: If oil is drawn out during the recovery
process,
the correct amount can be added directly from your
recovery-recycle-

recharge station
(if so
equipped)
prior to the charging
process.
It must be
stressed
that the need to protect
compressor
oil from
moisture is vital, observe
the procedures
in Handling Lubricating Oil.
Warning: Liquid refrigerant boils at -29°C (-20°F) at atmospheric pressure. Serious injury, even blindness, can occur if
the refrigerant comes into contact with the eyes.
Goggles and gloves must be warn while working with refrigerant.
First Aid
If refrigerant should contact the eyes or
skin,
bathe 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 eye specialist.
8-14 May 1996

^=2?
Air Conditioning
System Trouble Shooting
System Trouble Shooting
There are five basic symptoms associated with air conditioning fault diagnosis. It is very important to identify the area of
concern before starting a rectification procedure. Spend time with your customer on problem identification, and use the
following trouble shooting guide.
The following conditions are not in order of priority.
No Cooling

1.
Is the electrical circuit to the compressor clutch functional?

2.
Is the electrical circuit to the blower motor(s) functional?
3. Slack or broken compressor drive belt.

4.
Compressor partially or completely seized.
5. Compressor shaft seal leak (see 9).
6. Compressor valve or piston damag^ (may be indicated by small variation between HIGH & LOW side pressures
relative to engine speed).
7. Broken refrigerant pipe (causing total loss of refrigerant).
8. Leak in system (causing total loss of refrigerant).
9. Blocked filter in the receiver drier.

10.
Evaporator sensor disconnected?

11.
Dual pressure switch faulty?
Note:
Should a
leak or low
refrigerant be established as
the
cause,
follow
the procedures
for
Recovery-Recycle
-Recharge,
and
observe all refrigerant and oil handling instructions.
insufficient Cooing

1.
Blower motor(s) sluggish.

2.
Restricted blower inlet or outlet passage
3. Blocked or partially restricted condenser matrix or fins.

4.
Blocked or partially restricted evaporator matrix.
5. Blocked or partially restricted filter in the receiver drier.
6. Blocked or partially restricted expansion valve.
7. Partially collapsed flexible pipe.
8. Expansion valve temperature sensor faulty (this sensor is integral with valve and is not serviceable).
9. Excessive moisture in the system.

10.
Air in the system.

11.
Low refrigerant charge.
May 1996 8-17

Air Conditioning
/J=y>f^^^
—p )
System Trouble Shooting

12.
Compressor clutch slipping.

13.
Blower flaps or distribution vents closed or partially seized.

14.
Water valve not closed.

15.
Evaporator sensor detached from evaporator.
Intermittent Cooling
Is the electrical circuit to the compressor clutch consistent?

2.
Is the electrical circuit to the blower motor(s) consistent?
3. Compressor clutch slipping.

4.
Faulty air distribution flap potentiometer or motor.
5. Motorised in-car aspirator or evaporator temperature sensor faulty, causing temperature variations.
6. Blocked or partially restricted evaporator or condenser.
Noisy System

1.
Loose or damaged compressor drive belt.

2.
Loose or damaged compressor mountings.
3. Compressor oil level low, look for evidence of leakage.

4.
Compressor damage caused by low oil level or internal debris.
5. Blower(s) motor(s) noisy.
6. Excessive refrigerant charge, witnessed by vibration and 'thumping' in the high pressure line (may be indicated by
high HIGH & high LOW side pressures).
7. Low refrigerant charge causing 'hissing' at the expansion valve (may be indicated by low HIGH side pressure).
8. Excessive moisture in the system causing expansion valve noise.

Note;
Electrical faults
may
be more rapidly traced using PDU.
Insufficient Heating

1.
Water valve stuck in the closed position.

2.
Motorised in-car aspirator seized.
3. Blend flaps stuck or seized.

4.
Blocked or restricted blower inlet or outlet.
5. Low coolant level.
6. Blower fan speed low.
7. Coolant thermostat faulty or seized open.
8-18 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
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