Temperature measurements

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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.

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