Have a 06 Ford F150 Supercab XLT. 14500 miles on it. This past summer I had problems when turning on the ingition. It seemed to happen after the vehicle was parked, as I was at work, and when I returned with the AC controls on high the engine would not turn over. Whenever I turned the AC off it started. Since it has gotten colder down here there havent been any problems.
Other than that I have had no problems. The truck is still in mint condition, with regular oil changes and tire rotations, etc.
Any advice on the problem would be appreciated.
Thanks

 

Sounds like some grounding problem

 

It is possible the A/C compressor is seizing up since it will start fine when turning it off.