This 2005 F150 had no cold air when the A/C was on. The owner had taken it to another shop, but they couldn't figure the problem out. Eventually, he brought it back to me. A common issue is a worn A/C compressor clutch, causing excessive clearance between the clutch and the pulley, which was indeed the case with this compressor.

However, after replacing the compressor, the A/C was still not cold. I began diagnosing further and found no power to the compressor clutch due to a blown fuse caused by a short to ground on the circuit. Further testing revealed the circuit was shorted to ground due to the A/C compressor clutch circuit diode being installed backwards at some point. My theory is due to the diode being installed backwards, it eventually destroyed the diode which allowed current to flow freely in either direction, because even after reinstalling it correctly, the circuit was still shorted to ground.

I replaced the A/C compressor clutch diode and the fuse. Finally, the truck has ice cold air again!