If your truck has cruise, start by removing the single screw that holds the speed control module to the passenger side inner fender and set it aside. Then remove the blower fan from the HVAC plenum which is on the PS firewall. There are 3 or 4 screws and an electrical connector to remove from the blower. Once the blower is out of the way, clean out the leaves and twigs and use Lysol or similar if there is any mold/mildew inside the plenum. Reassemble. That usually takes care of it.
2003 FX4 Level II, Supercharged 5.0L V8, Headers, Duals
BW4406 manual transfer case, Aussie Locker, Torsen L/S, 4.10's
Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles
2003 XLT 2.3L M5OD-R1 reg cab beater, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid