1997 ASTON MARTIN DB7 air condition

Air Conditioning
Manifold Gauge Set 5=2?
Manifold Gauge Set
The manifold gauge set is a most important tool for
fault diagnosis and system efficiency assessment.
The relationship to each other of HIGH and LOW
pressures and their correlation to AMBIENT and
EVAPORATOR temperatures must be compared to
determine system status. Because oi the heavy
reliance upon this piece of equipment for service
diagnosis, ensure that the gauges are calibrated
regularly and the equipment is treated with care.
BLUE LOW SIDE RED HIGH SIDE
LOW

m
m

Manifold.

The manifold is designed to control refrigerant
flow. When connected into the system, pressure is
registered on both gauges at all times. During
system tests both the high and low side hand valves
should be closed (rotate clockwise to seat the
valves). The hand valves isolate the low and the
high sides from the centre (service) hose.
Low Side Pressure Gauge.
This compound gauge
is
designed to register positive
and negative pressure and may be calibrated as
follows:
• Full Scale Deflection - 0 to 24 bar pressure
in a clockwise direction
• Otol bar FSD negative pressure in a counter
clockwise direction.
High Side Pressure Gauge.
This pressure gauge may be calibrated from 0 to 34
bar FSD inaclockwisedirection. Depending on the
manufacturer, this gauge may also be of the
compound type.
Figure 1
The gauge set (Fig. 1) consists of a manifold fitted
with:

1 Low side service hose - BLUE.
2 Low Side hand valve - BLUE.
3 Low pressure compound gauge - BLUE.
4 High pressure gauge- RED.
5 High Side hand valve - RED.
6 High side service hose - RED.
7 System service hose - NEUTRAL COLOUR
(commonly yellow).
8-38 May 1996

^=2?
Air Conditioning
System Checking with the Manifold Gauge Set
System Checking with the Manifold
Gauge Set
Connecting the Manifold Gauge Set
Caution: Only use hoses with connectors which are
dedicated to HFC 134A charge ports.
Attachmentofthehosequick release connectors to
the high and low side
system
ports
is
straightforward,
provided that the high and low valves are closed
and the system is NOT operational.
Assessment ofthe system's operating system can be
carried out by using the facilities ofthe Recovery-
Recharging-Recycling station. Follow the
manufacturer's instructions carefully and closely
observe the safety procedures.
Warning: Under no circumstances should the connections
be made with the
system
in operation or the
valves

open. Should the valves be open and a vacuum
pump or refrigerant container attached, an
explosion could occur
as
a result of high pressure
refrigerant being forced back into the vacuum
pump or container.
Stabilising the System
Accurate test gauge data can be attained only if the
system temperatures and pressures are stabilised.
Ensure that equipment and its hoses cannot come
into contact with moving parts or heat sources.
It is recommended that a free standing air mover is
placed in front of the vehicle to provide mass air
flow through the condenser-cooling system.
Checking Procedure
Connecting the Gauge Set.
A test hose connected to the fitting directly under
the low side gauge is used to connect the low side
ofthe test manifold into the low side ofthe system,
and a similar connection is found on the high side.
When connecting the gauge manifold set to the air
cond ition i ng system an access va Ive core removi ng
tool is available for connecting the test hoses to the
high and low sides ofthe system.
Using the valve removing tool it enables the valve
core to be removed and held back inside the tool
eliminating restrictions and, thereby, providing a
full flow of refrigerant.
Warning: Do not open the high side hand valve while the
air conditioning system is in operation because,
high pressure refrigerant will be forced through
the high side gauge and to the refrigerant container,
if it is attached.
This
could cause the container to
rupture or the fitting at the safety container valve
to burst resulting in damage and personal injury.

1.
With theengineswitched off, remove the protective
caps from the schraeder valves.

2.
Fit the access valve removal tool to the schraeder
valves. Ensure that both the manifold hand valves
are in the closed position.
3. Connect the high pressure manifold gauge hose (to
the high pressure side of the air conditioning side of
the system (high side is always the line from the
compressor to the condenser). Connect the low
pressure or compound gauge hose to the low
pressure side ofthe air conditioning system.

4.
Using the access valve removal tool loosen and
screw out the valve cores.

1.
Start the engine and allow it to attain normal
working temperature then set it at fast idle (typically
1200 to ISOOrpm).

2.
Select full air conditioning performance.
3. With all temperatures and pressures stable or
displaying symptoms of faults, begin relevant test
procedures.
May 1996 8-39

Air Conditioning
System Checking with the Manifold Gauge Set D'^?
Purging the Test Hoses

1.
With the manifold test set attached to the system.

2.
Purge the high pressure test hose by cracking open
the high pressure side hand valve on the manifold
gauge set for 3 to 5 seconds. This allows the system
refrigerant to purge the air from the test hose and
discharge through the manifold centre test hose.
Immediately cl ose the high pressure side hand

valve.

3. Purge the low pressure test hose in the same manner
by cracking open the low pressure side hand valve
manifold gauge
set
for 3 to 5 seconds, then close the
hand valve.
Stabilising the System
The manifold gauge set is now attached to the
system and the test hoses purged of air. With both
hand valves closed, the system must be operated
for a few minutes to stabilise all pressures and
temperatures throughout the system in order to
obtain accurate test gauge readings.
Proceed as follows:

1.
Place all test hoses, gauge set and other equipment
away from all engine moving parts. Also keep the
hoses from touching the hot engine manifold.

2.
Start the engine and adjust engine speed to fast idle
3. Turn on the air conditioning and set for maximum
cooling with blower fans on high speed

4.
Open the car doors and/or windows (to quickly
eliminate car interior heat).
5. Operate the system under these conditions for 5 to
10 minutes to stabilise the system ready for testing.
6. Check the system for full refrigerant by noting the
sightglass indications. Some refrigerant loss occurs
over a period of time.
Note: The air conditioning
system
must contain a full
refrigerant
charge
before an accurate
system
check can
be
made.
An insufficient
charge
is indicated by
a stream

of
bubbles
or
foam.
If
the
refrigerant charge is low, the

system
must
be
fullydischarged into
a
refrigerant recovery
station and recharged with the correct weight of refrigerant
82.30.08. Do not top up a
system
with refrigerant.
Leak Test
A high proportion of ail air conditioning work
consists of locating and repairing leaks.
Many leaks are located at connections and are
caused by vibration. They may only require the re-
tightening of a connection or clamp.
Occasionally a hose rubs on a structural part of the
vehicle and creates a leak, or a hose deteriorates
which will require a replacement.
The specified maximum leakage rate at each fitting
is 0.5 kg of R 134a in 40 years and a leak detector
capable of operating to this accuracy must be

provided.
To check place the leak detector probe at
the lowest pointofeach joint, pausefortwo seconds.
Do not wave the probe about as refrigerant is
heavier than air and flows to the lowest point. If a
leak is greater than 0-5 kg in forty years is detected
identify the leak point for rectification.
Check that the leaking fitting has been tightened to
the correct torque. If the torque is low, rectify and
repeat leak test. If the torque is satisfactory,
depressurise the system, dismantle the leaking
connection and check the quality of the fitting.
If the fitting is satisfactory, clean and reassemble
after applying a thin film of refrigerant to the seat of
aflarefitting, ora newoiled "O" ring to an "O" ring

fitting.

Tighten to the correct torque.
Charge the system with 200 g of El 34A and leak test
the rectified system. If the system is satisfactory,
depressurise, evacuate and recharge the system.
If the system is unsatisfactory, i.e. leakage greater
than 0.5 kg in forty years, depressurise and replace
the leaking assembly.
8-40 May 1996

=2?
Air Conditioning
System Checking with the Manifold Gauge Set
Pressure Temperature Relationship.
Note:
Pressures
shown are under exact conditions
(see
test
conditions) and
are
not
necessary
true for every
car

checked.
Ambient Temperature is given as the air
surrounding the
condenser
and
is
taken 5 cm in front of
the
condenser.

Test Conditions.
Use a large fan to substitute for normal ram air through the
condenser. Engine adjusted to fast idle speed.
All conditions equivalent to 30 m.p.h. or 48 km/h.
Ambient
Evaporator
Temp °C
16
18
21
24
27
29
32
35
38
41
43
46
49
High
Pressure
Gauge
Reading
Ibf/in2
95-115
105-125
115-125
130-150

1
50-170
165-185
175-195
185-205
210-230
230-250
250-270
265-285
280-310
Low
Pressure
Gauge
Reading
Ibf/in2
10
12
4
16
18
20
22
24
26
28
30
35
40
45
50
55
60
65
70
Ten
-16
-14
-12
-10
-8
-6
-5
-4
-3
-1
0
2
5
9
11
14
17
19
21
Normal operating ambient temperature range is:
-24 to 43°C.
Normal operating evaporator temperature range
is:-12toO°C.
Under normal running conditions system pressure
should be, as follows:
Lowside:1.05to2.10kgf/cm21.034to2.06bar15
to 30 ibf/in2
High side: 13.00 to 14.40 kgf/cm2 12.75 to 14.34
bar185to205lbf/in2
Manifold Gauge Set Check Procedures
Refrigerant Slightly Low.
Complaint.
Little or no cooling.

1.

2.

3.

4.

1.

2.

3.

4.

5.
6.
7.
BLUE LOW SIDE
KED
HIGH SIDE
Condition.
The low side gauge reading is too low.
The high side gauge reading is too low.
A stream of bubbles evident in the sight glass.
The discharge air from the evaporator only
slightly
cool.

Diagnosis.
The system low on refrigerant due to slight leak.
Correction.
Test the system for leaks.
Depressurise the system.
Repair the leaks, and if necessary renew hoses or

units.

Check the compressor oil level. The system may
have lost oil due to leakage.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
Operate the system and check the performance.
May 1996 8-41

Air Conditioning
System Checking with the Manifold Gauge Set [n::S3^^?
Refrigerant Excessively Low.
Complaint.
Cooling is not adequate.
Air In The System.
Complaint.
Cooling is not adequate.
BLU£ LOW SIDE SlUE LOW SIDE MD HIGH SIDE
5.
6.
7.

Condition.

1.
The low side gauge is reading very low.

2.
The high side gauge reading very low.
3. No bubbles or liquid evident in the sight glass.

4.
The discharge air from the evaporator is warm.
Diagnosis.
System refrigerant excessively low. Serious leak

indicated.

Correction.

1.
Test the system for leaks.
Note: Partially recharge the
system
before testing the

system
for
leaks
to
ensure that leak detection is
obtained.
Depressurise the system.
Repair the leaks, and if necessary renew hoses or

units.

Check the compressor oil level. The system may
have lost oil due to leakage.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
performance.

2.

3.

5.
6.
7.
8-42
Condition.
The low side gauge reading
is
constant and does not

drop.
The pressure should drop until the compressor
cycles (thermostat control)
The high side gauge reading is slightly high (or
slightly lower especially if a large fan is used to
substitute ram air).
The sight glass is free of bubbles or only shows an
occasional bubble.
Thedischarge air from theevaporator
is
only slightly

cool.

Diagnosis.
Non condensables present in the system. Air or
moisturepresent instead of afullrefrigerantcharge.
Correction.
Test the system for leaks. Test the compressor seal
area very carefully.
Depressurise the system. Repair the leaks, and if
necessary renew hoses or units.
Renew the drier bottle, probably water saturated .
Check the compressor oil level.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
Operate the system and check the performance.
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

Air Conditioning
System Checking with the Manifold Gauge Set ffi:S5=27
After making the above checks operate the system
and check the performance. If the Condition is not

rectified.

1.
inspect the system for overcharge of refrigerant and
rectify as follows.
A. Discharge the system, until a stream of bubbles
appear in the sight glass and both gauge readings
drop to below normal.
B. Add new refrigerant until the bubbles disappear
and the pressures are normal. Then add 0.25 to 0.5

lb.
of additional refrigerant.

2.
Operate the system and check the performance.
If the gauge readings are still too
high.

3. Depressurise the system.
3. Removeand inspectthecondenserforoilclogging.
Clean and flush the condenser to ensure the free
passage refrigerant or renew the condenser.

4.
Renew the receiver-drier.
5. Evacuatethesystem using
a
vacuum pump Recharge
the system with new refrigerant. Operate the system
and check the performance
Moisture in the System
Complaint.
Cooling notadequateduringthe hot part of theday.
Note: Cooling may
be satisfactory
during
early
morning/

late evening
but
inadequate
during
the
hot part of
the
day.

BLUE LOW SIDE RED HIGH SIDE

1.

2.

3.

4.

5.
LOW
Condition.
The low side gauge reading normal but may drop
into vacuum during testing.
The high side gauge reading normal but drops
when the low side drops into vacuum. The sight
glass may show tiny bubbles.
The discharge air from the evaporator is cold but
becomes warm when the low side gauge drops into

vacuum.

Diagnosis.
Excessive moisture in the system.
Desiccant agent saturated with moisture which is
released during high temperatures. The moisture
collects and freezes in the expansion valve which
stops the refrigerant flow.
Correction.
Depressurise the system.
Renew the drier bottle.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
Operate the system and check the performance.
8-44 May 1996

=2?
Air Conditioning
System Checking with the Manifold Gauge Set
A Large Amount of Air in the System.
Complaint.
Little or no cooling.

1.

2.

3.

4.

5.

BLUE
LOW SIDE RED HIGH SIDE
Condition.
The low side gauge reading is too
high.
The high
side gauge reading is too
high.
An occasional
bubble in the sight
glass.
The discharge air from the
evaporator is not
cool.

Diagnosis.
Air in the system. The refrigerant contaminated by
non-condensables (air and/or moisture).
Correction.
Depressurise the system.
Renew the receiver-drier.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
Operate the system and check the performance.
Expansion Valve Malfunction.
The valve stuck open.

1.

2.

3.

4.

5.
6.
BLUE LOW SIDE
HIGH
Complaint.
Little or no cooling.
Condition.
The low side gauge reading is too
high.

The high side gauge reading is normal or slightly
low.
The discharge air from the evaporator is warm. The
suction hose and the evaporator show signs of
heavy sweating.
Diagnosis.
The expansion valve allowing excessive flow of
refrigerant through the evaporator coils causing
flooding of the coils.
Correction.
Depressurise the system.
Renew the expansion valve.
Renew the drier bottle.
Evacuate the system using a vacuum pump.
Recharge the system with new refrigerant.
Operate the system and check the performance.
May 1996 8-45