2001 f250 4x4 diesel a/c distrupution system works fine vent

When AC on and cold air from rear but not front is usually a blend door/heater box issue. You may have a non functioning blend door motor that controls hot/cold distribution of airflow

your thermostat may have a cooler temperature try changing it for a hotter setting

the heater & defroster baffles are controlled by electic motors that open and close the baffle (doors) to let the air to the heater and defroster vents. the motor must be bad

If you don't hear a thud or noise of a flap opening or closing when switching between hot and cold then a lever is probably broken.

Had the same problem on 98 Eddy Bauer we have. Have you noticed that it has a tendency to belch out hot air and the blower speed slows down mostly when you accelerate or give it a little more gas to climb a hill or an overpass or even pass somebody? If this is the case there is a pressure switch that's hooked into the intake manifold were it can sense a drop in pressure and when it does it drops the ac clutch out and slows the dash blower down till the pressure comes back up. JUMP IT OUT. All your problems will go away. Thats in there to unload the engine during acceleration and heavy loads and after the switch ages it gets trigger happy and lazy about closing to bring the ac back on.

Pat - Houston

Hi...
Perform the following basic Checks and Information
1. Check Drive Belts,If belt is intact proceed to the next step.
2. Check for Compressor Clutch Engagement - Turn the air conditioner to the "on" position and set controls to the coldest setting. Start the engine and allow to idle. Then open the hood and inspect the clutch at the front of the compressor, is it turning? "Engaged" if so, the system has enough refrigerant to activate. If the system is low on refrigerant it will not work properly. In this case an air conditioner recharge kit is needed to recharge the system. If the compressor clutch is not turning proceed to next step.
3. Inspect for Refrigerant Leaks
4. Check under dash panel and under hood power distribution center
5. Check Temperature Control Vents - The vents inside your car are controlled by a cable, electrical servo or vacuum servo. If the vent door is not functioning properly it will cause warm air from the heater to exit the vents. To check this start the car and allow the engine idle, next turn the blower motor speed on low, switch the temperature control from warm to cold while your ear is close to the vents. You should hear the door move inside the heater box as it swings from open to close. If not, inspect for a vacuum leak or a shorted motor in the servo, repair the leak or replace the servo motor.
Thanks
Smith

Check for a vacuum leak. WHERE is the magic question.

Yeah Ron, the flap that covers the heater core is open and when you're moving the air is pushed over the heater core and into the cab your in. Possibly just a vacuum line of that controls said flap. Check all vacuum lines for good proper connection to these flaps because all of them are vacuum actuated.

fault temp sensors
still can be a worn or stuck shaft flap at the actuators
or actuators is still faulty