Don’t do things by half
13 September 2013 
Air conditioning repair is not something we focus on at the workshop. We don’t have an AC machine or equipment and we haven’t done F-gas training. If the need arises, we call upon one of our garage neighbours who are happy to perform the gas-centric element of the system for us (degas, vac, leak detections and regas), at a very reasonable rate.
My first thoughts were why would you specialise in air conditioning and not want to get involved in a repair? Then I supposed it is akin to doing diagnostic plug-ins. For a £60 fee, an AC re-gas with a fixed time and a materials cost of around 10% seems like great, easy business. However, consider doing the repair – open ended time, unknown cost. Hmmm… this is slightly more difficult business. As a customer, I would wonder why a garage could do the easy parts of the air con system but could not do the rest. ‘Capability’ alarm bells would be ringing.
The vehicle arrived on the appointed day and I began to look through the system. A quick visual inspection didn’t show any obvious issues. I attached the Autologic diagnostic equipment and reviewed the codes and data within the air conditioning system. The system had set a hard trouble code for pressure sensor plausibility, so this was the place to start. A look at the live data showed that the pressure was at zero bar, so time to check out the output voltage from the pressure sensor.
I physically examined the loom along its length looking for a break and found that the loom, where the spur of loom for the sensor joined the main loom, had become completely detached and was held together by the insulating tape wrap. Interestingly, both of these loom failures appeared to have been caused by poor quality wiring or a lack of appropriate strain relief. I measured at the loom side stubs of wire and picked up ground and 5V readings. This suggested that the loom from this point back to the air conditioning computer was good. So, after checking the sensor loom for additional damage, I made another splice repair to the main loom. Now I had power (5V) ground (0V) and signal (0.5V) at the pressure sensor, figure 3. The system now had the capability to report on the high pressure. Using my diagnostic platform I reset the system and cleared and checked the trouble code, which thankfully stayed cleared. Next was to check live data and the system’s operation.
I set the aircon to cold and the internal fan to fast, whilst watching the live data. The pressure was still reading zero bar. This was strange, the sensor now had the capability to report pressure and it was reporting zero pressure. The compressor (a variable displacement type – so no magnetic clutch) showed on the data stream as being inactive (0%). Also, the cooling fans didn’t cut in. The system definitely wasn’t functioning. The strange thing was the reading of zero pressure. Remembering that the customer stated he’d had the gas ‘done’, I was unsure if the pressure reading was true, i.e. there was zero bar in the system or if the sensor or system had a subsequent fault.
So, I had to measure the pressure and fortunately my neighbouring garage helped me with this. The result was a big fat zero – no gas, hence no pressure. We did a leak check, thinking there’d have to be a pretty big leak for the all of the gas to escape within a week – no leak detected. I called the customer as he was going to have to pay ‘again’ to have the vehicle re-gassed before I could prove the wiring repair had addressed the root cause of the problem. “You’re going to have to pay to have your system recharged,” I said, adding that I recommended that he went back to the other place to try and get his money back. The customer replied “Oh, I didn’t pay the other place. They run a deal where if they top the gas up and the system doesn’t work, they don’t charge anything”. The penny dropped. The first workshop had recovered the gas, vacuumed the system (leak test) and then recharged it. When the system failed to operate they recovered all of the gas and sent the customer, now completely devoid of refrigerant on his way… How can they make this kind of trick pay?!