I am writing as a follow-up to the issue with the (petrol-powered!) Clio air-conditioning and to whether it would automatically self-activate. Well, I recently purchased a three-year old VW Passat 2.0 TDI 140 with the manually controlled Climatic system. I also thought that there might be something wrong with it, as when you turned on the blower switch, the air-conditioning would sometimes come on, with the A/C button then illuminating. This could then quite easily be turned off, but I thought that it was a little disconcerting. After some research on the internet (the Passat handbook was of no help), I then discovered that this was apparently a design feature to ensure that the air conditioning gets used periodically, to circulate the refrigerant and lubricate the seals. There are apparently two sensors: one for the temperature, so that when the desired level is reached the temperature is then automatically reduced, and the other for the humidity such that, with the air direction set to the windscreen, the air conditioning will activate automatically when the blower switch is turned on. I have never known this before, and I do not want manual heating controls working in a semi-automatic way, especially when there is no mention of this feature in the handbook. If it is to ensure periodic use of the air conditioning, then surely the manufacturer should make this clear?
That is a very interesting piece of information Malcolm, and something of which, as you may now guess, I was quite unaware. Big brother knows better! But I do have to say that it probably is quite a good idea really, as a good proportion of air conditioning problems are the result of extended lack of use of the A/C function. Such systems, like the lane deviation systems that I loathe, are, of course, generally designed for idiots and bad drivers, not Diesel Car readers! As you say though, this automatic air conditioning turn-on feature really should be pointed out in the handbook. Thanks for the information though. I believe that more recent Climatic systems have now dumped the temperature markings (18, 22, 26) and just now have a knob that rotates between blue (minimum) and red (maximum) which presumably still represent the same temperature ranges. Thanks for the info, Malcolm.