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Help without the con

By autotech-nath on April 23, 2024

Diagnosing air conditioning issues can be tricky but Rob Marshall seeks assurance that technicians need not feel on their own.

While it tends to be easier to diagnose an issue on something you can see and touch, the sealed and isolated internals of thermal management systems are somewhat more challenging. Fortunately, you are not left to struggle unaided when diagnosing problems as we approach peak air conditioning repair season.

Back to basics…

As with many systems fitted to cars, the air conditioning system is becoming more complex. Naturally, the advent of high-voltage propulsion has encouraged the HVAC circuit to evolve into thermal management for the running gear. This is not the only consideration. Even the simpler air conditioning systems have not escaped the never-ending drive for efficiency.


Denso advises that there is not one good
full-proof method for leak finding and electronic refrigerant leak detectors (such as that pictured) must be calibrated annually.

Sadly, this is making them more sensitive to issues. Nissens, for instance, has noted that components are becoming lighter and impurities impact the air conditioning much more so now than in the past.

Nissens reasons that the best help a technician can have is a decent grounding in air conditioning fundamentals. The company reasons that workshop staff cannot diagnose, service, or repair the system properly without a basic understanding of the relationship between temperature and pressure. To assist the aftermarket, Nissens offers three levels of training, with Level 1 covering these basics, which underpin the more advanced courses that follow.

Denso also impresses the importance of training. It provides coaching to its distributors, who can invite workshop technicians to attend. It also structures its teaching as starting with the fundamental theories that are necessary for the more complex diagnostic procedures that feature in the advanced courses.


Aftermarket tools that support your diagnostic process include tools that facilitate pressure and temperature real-time measurements, without accessing the EOBD socket. For more information, see https://bit.ly/3ViZi4e

Sniffing out the problem…

Training also helps technicians select the most appropriate diagnostic technique and tools. Denso highlights the three most common methods of detecting refrigerant leaks:

Ultra-violet (UV) dye remains a common addition. Yet, it can affect the lubricating performance of the oil; adding too much can have detrimental consequences for the air conditioning system’s long-term health. Denso advises that technicians use an SAE-approved dye, based on the correct compressor oil type.

An inert gas (such as nitrogen or Form gas that is 95% nitrogen and 5% hydrogen) can be employed to pressurise the AC system, while a soap solution is sprayed on the suspect components to see if bubbles form.

Finally, an electronic refrigerant leak detector can be employed for inaccessible areas, such as within evaporators.

Nissens draws technician attention to two of its tools that facilitate quick and right-first-time diagnostics. Its wireless pressure and temperature diagnostic equipment permits data to be displayed on the technician’s mobile phone. This flexibility allows the diagnostic procedure to be performed regardless of where the technician stands. Therefore, parts of the air conditioning system can be controlled diagnostically, while allowing the technician access to more accurate direct temperature and pressure changes as they occur. Should you wish to discover more about the methodology, check out: https://bit.ly/3Tji2hd and https://bit.ly/3TB6tDx

As with many things in life, the simplest options are often the best. A fascinating tool from Nissens is a visual inspection sight glass, see over page. It provides an insight into the normally sealed system, as it operates. With it, you can identify foreign contaminations that might be the source of your problems. These include those formed by the reaction of consumables within the closed circuit, such as crystalising leak stops, excessive UV dye quantities, or signs of burnt oil that indicate compressor overheating.


UFI highlights that some condensers are cooled by coolant, not air. The main advantage is that liquid cooling reduces the refrigerant capacity and makes the air conditioning system more compact.

Turning up the heat: HV

The Heat Pump on high-voltage vehicles introduces new challenges. Nissens reports that, while the tools used are, generally, the same as those used with R134a refrigerant, systems that run on R744 (CO2) have operational pressures of around ten times higher. This means that special tools are needed, coupled with supplementary training. Nissens highlights its dedicated module on Heat Pumps, along with its online library at www.nissens.com/experts This platform is free and allows garages to share data, stories, pictures and videos that are dedicated to the understanding and diagnostics of AC systems, including thermal management systems.


Nissens’ visual inspection sight glass gives you the best chance of seeing what goes on inside the normally sealed refrigeration circuit. To learn more, see: https://bit.ly/3TwGey5

Why the machine cannot do it all…

While it is true that air-con machines are automatic, they are as good as the technician operating them. Nissens reasons that such equipment still follows instructions that are entered by the technician at
the start of the process. Furthermore, the automatic procedure will need constant monitoring throughout the cycle. For instance, a maladjusted solenoid valve, an incorrectly calibrated scale, or a lubrication-starved vacuum pump can cause false readings, fooling you into thinking that there is a leak, for instance. Ironically, Nissens advises that, the more automated a machine is, the more critical technicians have to be about the display readings.

Denso agrees that the lack of knowledge about these machines and basic air conditioning principles is causing mistakes. These range from technicians adding excessive quantities of oil/UV-dye, selecting an insufficient evacuation time, or even overfilling the system. Other basic housekeeping errors include dosing contaminated oil, because the fresh oil bottle is not refreshed daily, plus either inadequate, or zero air conditioning machine maintenance. Again, both companies highlight the importance of training to prevent these issues from arising.

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