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I have an 08 451 for two. The automatic temperature control stopped working years ago, as I understand most of thelm did. Since then, I have had only hot or cold, which I could live with by varying the fan speed. Recently I have an additional problem....with the heat control in the fully "up" position, I get max heat, but at odd intervals it starts blowing cold (or semi-cold) air. By moving the lever down and back up to maximum quickly, hot air resumes. ( I assume the problem is associated with an air diversion vane.) Has anyone else had this problem, and found a solution? Don't want to get too involved without a little more information as to what's involved. On the same subject....has anyone succesfully restored one of these 08 or 09 controls to their original automatic temperature regulatiflunction? They really worked great when they were new!
 

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I've had problems with heat in my 2008 for the past few years. Driving along hot air will be blowing then all of the sudden start blowing cold. Very annoying when it got colder than -20'C. Even had the same issue as you where moving the heat control to the top would blow cold and moving it down 1 click would be hot.

Last week I lost heat completely. Car was up to temp and no heat at all. I remembered something about a sensor in the passenger footwell. I turn on my flash light and stuck my head under the dash and saw the wiring harness to temp sensor in the air box was mangled. I pieced together a new harness and now my heat works perfectly.

From what I understand there are 2 sensors for the temperature control system; 1 in the air box that measures the temp of the air coming out of the heater/ac and then there is another sensor that monitors the cabin temperature. I don't know exactly where that 2nd sensor is but I think it is built in to the heater control module (the thing on the dash with the fan speed selector and heat temp slider). If that infrared sensor is bad then you need to replace the module. They are on ebay for cheap.
 
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