Temperature measurements

iklan bawah share

Measuring the temperature at various points on the A/C system and making comparisons provide 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 provides 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 temperature probes and varying the blend door position allow the technician to verify the available 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 condenser 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 (T)’ check which is mainly used on FOV systems where access to the inlet of

Table 4.1

the evaporator is available. Record the temperature of the inlet and outlet of the evaporator and compare the results with a chart that indicates the amount of refrigerant which is required to be added to the system. A large difference indicates the inability to transfer a large quantity of heat. This is due to low refrigerant charge. The most accurate method of determining the charge level is to recover the refrigerant and check the weight. Only this method is recommended.

A system under a small cooling load may still be able to produce a low temperature out of the centre vents but when placed under a high load may fail to provide adequate cooling performance. Measuring temperatures around the system and making comparisons allow the technician to evaluate how much load the A/C system is under and how it performs under that load.

iklan bawah postingan

Initial Vehicle Inspection

iklan bawah share

The initial vehicle inspection is not a checklist. Information from the customer on the symptoms, 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 replicated 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 system (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.

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 operate, 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: 900–1000 rpm.

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 temperature 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.

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.

iklan bawah postingan

Diagnostics and Troubleshooting

iklan bawah share 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.

iklan bawah postingan