By Rob Marshall
1. Check the high and low-pressure readings and measure air temperature at the interior vents. Doing this alone does not guarantee that the system is in good working order, so consider performing the following steps as well.
2. Using an infrared thermometer, measure the compressor body temperature with its clutch engaged (if one is fitted), after it has been running for at least five minutes. At 20°C, your reading should be approximately 50-60°C
3. Again, using your thermometer, check temperatures at the inlet and outlet ports on the condenser and note that the difference between your readings should be around 30%. 4. Checking for contamination requires fitting a Visual Diagnostic Tool to the air conditioning system’s service ports. If in good condition, you should see a light green colour through the inspection glass. Brown/black liquid indicates that the system has overheated. Rubber, plastic, or metal particles point to excessive wear, or imminent component failure. Bubbles may designate excessive moisture. Consider also that the PAG lubricating oil absorbs moisture and tends to be left behind, when the gas escapes. You will also be able to identify poor-quality previous repairs. Nissens provides more detailed information in this downloadable booklet.
5. From this stage, you may wish to obtain permission from the car owner, who might challenge about extra work being performed on their air conditioning, which seems to work satisfactorily. However, you cannot check if the correct amount of refrigerant is present without recovering it from the system, because it is measured by weight and not by the earlier pressure readings.
6. As with all regassing exercises, vacuuming the system removes moisture/air from the circuit. If you noticed excessive quantities in Step 4, you may wish to replace the dryer, presuming it is accessible and separate to the condenser. Otherwise, the entire condenser will need to be renewed.
7. While the system is under vacuum, make visual inspections for leaks, including tubes, hoses, condenser, receiver drier, compressor and all joints. Look also for corrosion, especially between aluminium and steel components.
8. Due to their position in front of the radiator, condenser cooling fins are vulnerable to impact damage and corrosion. If you can reach it (with the engine off) remove any accumulated organic matter, such as rotted leaves. Run a blunt tool (do not poke) very gently across the lower fins especially; should they turn to dust and/or disintegrate, the tiny passageways will be unsupported, making them liable to fracture. Do not be tempted to recharge systems with deteriorated condensers. Be very wary that electric cooling fans could restart suddenly; disconnect the relevant fuse, or electrical connector to avoid risking a severe injury.
9. Only if it is holding vacuum (i.e. negative pressure), can you recharge the system. Once filled with the specified weight, measure the temperatures at the air vents with the system running and repeat Steps 1-3.
10. Annual cabin filter renewal is also essential to ensure optimum efficiency of the heater and ventilation system. Should the filter be blocked, it could be possible that this will place extra strain on the blower fan motor and resistor pack.
Read the full article in the May 20 edition of Autotechnician magazine, here.