Purging The Test Hoses; Leak Test - Aston Martin DB7 Workshop Manual

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 w i l l 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