I have the same problem... For mine it is more like 1,2, 3 1/2 then 4 lol. The culprit in question is the knob itself. I took off the dash and figured out that the knob is broken so it is essentially misaligned hence the "skip" from 3 to 4. As for a fix I'm guessing you would just have to replace the knob which I don't know if replacing just that is possible and not getting the whole bottom control unit for the ac controls. It is an easy fix. Just remove the dash and unplug all the connections, swap control units then plug everything back in. You could do a search for the dash removal if you do not know how. And search online or at a local junk yard for the part. Hope this helps.
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