It is unusual to be asked to investigate an A.C. (Air Conditioning) fault in the middle of November but that is exactly what happened recently. The vehicle was a 2008 Volkswagen Touareg which had been recently purchased by the customer who had then noticed that the A.C. was inoperative, I was asked by the selling dealer to fix the problem.
The job was allocated to my son Scott who began by checking the refrigerant static pressure, this is done by connecting manifold gauges to the A.C. high and low pressure connectors, because the vehicle is equipped with a low pressure cut-out switch we needed to establish that the static pressure was sufficient.
As the pressure equalises when dormant you would expect to see approximately the same pressure in both high and low circuits, although refrigerant pressure will differ due to ambient temperature at this stage there was no need to be so precise and the pressure in the system was found to be sufficient.
Next to check that the actual pressure matched the figure displayed in the climate control module by monitoring the live data display of the refrigerant pressure sensor this was found to match the actual figure. There are numerous reason why compressor cut-out can be activated so further investigation was required.
As there were no error codes logged in the module the next step was to scroll through the individual component live data streams to look for any abnormalities.We soon came across the fresh air temperature sensor display which portrayed a figure of -18°C (clearly incorrect).
After removing a few components from within the cabin we located the sensor in the fresh air intake duct (see photo), could this be the problem?
At this point Scott suggested an experiment, he suggested we warm the sensor, monitor its reading and note if the A.C. begins to function. He gently heated the sensor with a hot air gun, we immediately saw a rise in temperature and once in the plus figures the A.C. compressor cut in and the A.C. system became operational. This would appear to confirm our suspicions.
A new sensor was obtained, installed in the vehicle and immediately A.C. functionality was restored. The owner was happy as was the selling dealer that the fault wasn't anything too serious.