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4
Diagnostics
and
troubleshooting
The aim of this chapter is to:
Enable the reader to understand the range of techniques that can be used in diagnosing
faults which affect system performance.
4.1
Initial vehicle inspection
The initial vehicle inspection is not a checklist. Information from the customer on the symp-
toms,vehicle history and conditions upon which the fault occurs will allow the technician to be
selective.The technician should first try to gather as much information as possible and assess
if the symptom is normal behaviour (water dripping from underneath the vehicle) or not.The
technician should then assess if the environment in which the fault occurs can be replicated.
For example, a fault which occurs when the vehicle has been idle for 2 days cannot be repli-
cated the same afternoon the vehicle has been delivered.The correct conditions (temperature,
load conditions) must be available to enable accurate fault detection. If conditions are not
right then the customer must be aware that an initial diagnostic period will be allocated to the
vehicle to carry out a range of tests allowing a number of possible causes to be verified.
The technician should then ensure that they have access to all information required from
the customer and for the vehicle.This includes fault finding charts, wiring diagrams, technical
service data,diagnostic procedures,technical service bulletins etc.This information may be as
simple as a radio code in case the power to the vehicle is interrupted to ensuring the customer
has access to a fault code pod (card) which allows access to any fault codes held within the sys-
tem (see Chapter 3,sections 3.8,3.9 and 3.10 for examples of information).Manufacturers also
have software-based fault diagnostic procedures which direct the technician through guided
procedures.Technical helplines are also available.
Note – if the technician is inexperienced,then use the inspection as a checklist.
Simple inspection routine
CHECK CONDENSER FINS FOR BLOCKAGE OR DAMAGE
If the fins are clogged,wash them with water.
Note – be careful not to damage the fins.
CHECK THE POLLEN FILTER FOR SERVICE CONDITION
If dirty remove and replace.
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MAKE SURE THAT DRIVE BELT IS INSTALLED CORRECTLY
Check that the drive belt fins fit properly in the ribbed grooves.
CHECK DRIVE BELT TENSION
Check the drive belt tension.
CHECK CONDENSER FAN FREELY ROTATES
Note – after installing the drive belt,check that it fits properly in the ribbed grooves.
CHECK ENGINE COOLANT LEVEL
Check coolant level.If unsatisfactory then test coolant system.
START ENGINE AND TURN ON A/C SWITCH
Check that the A/C operates at each position of the blower switch.If blower does not oper-
ate,check electrical circuits.
CHECK MAGNETIC CLUTCH OPERATION
If magnetic clutch does not engage, check system pressure with gauges and power supply
and operation of A/C control,e.g.electrical operation of low pressure switch.
CHECK THAT IDLE INCREASES
When the magnetic clutch engages,engine rpm should increase.
Standard idle-up rpm:900–1000rpm.
CHECK THAT CONDENSER FAN MOTOR CUTS IN
CHECK THAT THE HEATING PIPES LEADING TO THE HEAT EXCHANGER
ARE HOT
CHECK THE PERFORMANCE OF THE A/C CONTROLS
Check the air distribution control, vary the direction of the air distribution and check air
flow.Vary air temperature to test blend operation. Use a temperature probe to verify tem-
perature range (4–60°C) and air direction (panel,floor,face).
The initial vehicle inspection should direct the technician to one of the following:
1. A performance diagnostic test on the A/C operation:
A/C performance test.
Pressure gauge analysis.
Temperature measurement on A/C components.
Refrigerant identification test.
Level of refrigerant charge.
Recovery.
Leak testing – OFN,bubble,vacuum,UV dye.
Recharge and retest.
2. A/C electrical tests:
Self-test checking for fault codes via control panel LCD/graphics display.
Serial test using a handheld tester – wiggle test,actuator,DTC,data logger.
In-depth ‘pin-by-pin’ electrical test using a break-out box or directly from the module
connector.
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Automotive Air-conditioning and Climate Control Systems
Note – systems with a fixed orifice valve and cycle switch (CCOT) are controlled mainly
by pressure measurement. This means that pressure type tests like cycle tests are well
suited to diagnosing system faults. Systems like TXV which are controlled by measuring
temperature are well suited to all gauge and temperature tests.
4.2
Temperature measurements
Measuring the temperature at various points on the A/C system and making comparisons pro-
vide the technician with valuable information on system performance.
Pinpoint temperature measurements
Measuring the temperature of the refrigeration components at certain points around the A/C
system allows the technician to verify the changes occurring within the system.Table 4.1 pro-
vides a guide to the temperature of the refrigerant flowing through the components within the
A/C system.
Measuring the temperature of the air flowing inside the vehicle at certain points allows the
technician to ensure the blend and air distribution system is functioning correctly.Placing tem-
perature probes and varying the blend door position allow the technician to verify the avail-
able temperature range the system is capable of delivering and how quickly the range can be
delivered. Measuring the temperature and rate of air flowing at different ventilation points
tests the air distribution positions.
Temperature comparisons
Some important temperature comparisons:
1. Ambient temperature and condenser temperature.
2. Centre vent temperature and the ambient temperature (minimum difference of 20°C).
3. Temperature of the high and low pressure side of the A/C system.
4. Inlet and outlet of the condenser (difference of 15–30°C). Excessive difference indicates a
blockage similar to the action of an orifice tube. A small difference indicates that the con-
denser efficiency is low. Parallel condensers are measured from left to right and serpentine
condensers from top to bottom.The temperature difference must be progressive.
5. Inlet and outlet of the evaporator (maximum difference of 4°C).This is also referred to as
the ‘Delta T (DT)’ check which is mainly used on FOV systems where access to the inlet of
Table 4.1 Surface temperature of A/C components
No.
Description
Temperature
1
Compressor
Up to 80°C
2
High pressure connection
Up to 80°C
3
Condenser
Up to 70°C
4
Dehydrator
Up to 60°C
5
Relief valve
60°C reduced to 24°C
6
Evaporator
Warmer than 24°C
7
Low pressure connection
Warmer than 24°C