The air conditioning systems on some 2007-08 4.6- or 5.4-liter Ford F-150 and Lincoln Mark LT pickup trucks may stop working when the ambient temperature is greater than 110°F.
According to Ford, the condition usually occurs when the vehicle is stuck in bumper-to-bumper traffic for at least 15 minutes with the transmission in gear, and is due to the PCM deliberately disengaging the compressor clutch to protect the compressor from damage in the high ambient temperatures noted.
Replacing the A/C compressor pulley, the water pump pulley and the heater core feed hose clamp near the right/front portion of the engine with revised parts is the only surefire fix. All are designed to provide extra cooling from the A/C system once the compressor clutch does engage.
Here are the part numbers for the new-design parts: Compressor pulley (7C3Z-19D784-A), Water pump pulley (F6TZ-8509-AA), Heater core hose clamp (W709811-S900).