2011 Ford F-150 Lariat A/C problem

The compressor clutch has to engage to turn the compressor and enable AC. There is a coil behind the clutch that acts as a magnet when it receives the electrical signal to engage the compressor in order to pull in and engage the clutch. This coil can wear over time and become less effective at pulling in the clutch. It could also simply be too large of an air gap between the compressor and the clutch so it is more difficult for the clutch to engage. It could also be a combination of both.

You could try removing the compressor clutch and taking out a shim (basically a tiny washer) to reduce the air gap. A quick google for your specific vehicle model AC compressor clutch gap specs may tell you how big this air gap should be, and you could check it with feeler gauges to see if it is within spec.

If your AC compressor is somewhat accessible, you could try giving the clutch a quick tap with the handle of a screwdriver or mallet or similar while the engine is running and AC on max, and see if it will make the clutch engage.

The next step would probably be a new AC compressor clutch kit, which would probably include the clutch, coil, and shims to replace it. This would probably be around $200 for the parts, so consider checking the air gap if possible before going this route.

I had a similar experience where the AC would not engage for a while and since my AC compressor was right on top and easily accessible, I could give it a smack with a screwdriver handle and it would kick right on and work again. Finally replaced the clutch as mentioned and haven't had an issue since.