Your heater core has failed.
If there is no heat coming out of the vents, but there is air coming out on a 2003 Mercedes Benz E-320, check the thermostat to make sure it is not sticking. If this is okay, check the heater core. If the heater core is bad, there will be water on the passenger side floorboard.
Most likely you have a blown had gasket.
needs a sensor in the reservoir
Ford Dealer can help you. And tell you if there is anything wrong with your 2003 F150.
If it blows only out the defroster vents : then check for Vaccume leak Rick ASE L-1 Master TransMichigan.com
1st bet: Does it smell like antifreeze? Leaky heater core. 2nd bet: Worse after rain or car wash? Leak under cowl vents (the vents in front of the windshield. Good luck!
Without testing a guess would be a blend door or actuator or maybe a control problem
Try closing the air vents or set them to recirculate before switching off the engine.
Dexcool
Red.
In the radiator.
A 2003 Ram uses red, five year antifreeze.