Not hot air whn control is moved to hot

Sounds like driver side blend door is not functioning, either actuator bad or door has broken, remove actuator see if door moves freely, if door moves freely test actuator, leave out and connect wiring, move controls from cold to hot see if actuator moves.

Sounds like possibly the blend door is broken inside the heater box, I would double check and make sure the coolant level is full, if it is I would take the actuator off on the blend door and try and move it by hand and see if it changes

check HVAC fuse.if fuse okay heater control module could be the problem.

Air Temperature Control Blend Door Failure

In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car.

Air Temperature Control Blend Door Failure

In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car.

If the actuator is moving when you move the control it may be a broken or warped plastic door. If the actuator does not move look for a bad control unit or a vacuum leak.

Do the two heater core supply hoses get hot where they go through the firewall to the heater core? If one is hot the other cool to the touch then you have a plugged heater core flush it out with a garden hose, if they are both hot then a part called the air temperature control blend door is not moving inside the air ducting due to it being warped and jammed and/or the actuator that moves it being defective, to replace the blend door and its actuator requires the dash be removed from the truck to access the air ducting that contains the blend door.

The temperature of the air coming out of the ducts is controlled by a door that moves between the heater core and the AC core, it is called the "blend" door for obvious reasons as it blends the hot and cold air streams to give the desired air temperature at the dash vents. The door is controlled by a small gear drive DC motor called the blend door actuator, what happens in most case is the actuator is damaged by a blend door that is warped from heat being hard to move or not moving at all which is the case with your truck. The blend door and its actuator should be replaced as one repair, the dash must be removed from the truck to access the air ducting that contains the blend door, you absolutely need a service manual to complete this job, it takes about 10 hours.

first, check under te hood to see if the heater core water hoses are hot going in and coming out. If hot going in but cold coming out, water valve (if you have one) may not be working.
------------------------------------------------------------------------------------------------
Control System Outputs
The air management doors are controlled by vacuum control motors (18A318) and an A/C electronic door actuator motor (19E616). The air inlet and distribution doors are controlled by vacuum control motors. The temperature blend door is controlled by the A/C electronic door actuator motor.
The A/C electronic door actuator motor provides a variable number of temperature blend door positions. Temperature control position energizes the A/C electronic door actuator motor moving the temperature blend door.
Vacuum control motors are used on both air distribution and air inlet doors. The air inlet and panel/defrost doors use a two position vacuum control motor. The floor duct/panel door uses a three position vacuum control motor. Vacuum control motors are controlled by engine vacuum through the climate control head.
For more information on the control components Section 412-04 .
-------------------------------------------------------------------------------------------------------------------------------------
Air Management Doors
The air management doors are controlled by vacuum control motors (18A318) and an A/C electronic door actuator motor (19E616). The air inlet and distribution doors are controlled by a vacuum control motor. The temperature blend door is controlled by the A/C electronic door actuator motor.
The A/C electronic door actuator motor provides a variable number of temperature blend door positions. Temperature control position energizes the A/C electronic door actuator motor moving the temperature blend door.
Vacuum control motors are used on both air distribution and air inlet doors. The air inlet and panel/defrost doors use a two position vacuum control motor. The floor duct/panel door uses a three position vacuum control motor. Vacuum control motors are controlled by engine vacuum through the climate control head.
-------------------------------------------------------------------------------------------------------------------
Section 412-04: Control Components - Climate Control 1997 F-150, F-250 Workshop Manual
REMOVAL AND INSTALLATION A/C Electronic Actuator
Removal

1. Remove the floor duct panel.
   • Remove the two plastic push pins (one each side) and release the expander clip.

1. Remove the RH instrument panel brace.
   1. Remove the lower nut.
   1. Remove the upper bolt.
   1. Remove the brace.

1. Remove the LH instrument panel lower nut and position brace out of the way.

1. Disconnect the vacuum harness from the vacuum actuator.

1. Remove the floor duct.
   1. Remove the two screws (one each side).
   1. Remove the floor duct.

1. Remove the panel/floor door vacuum control motor.
   1. Disconnect the vacuum line connector.
   1. Remove the two panel/floor door vacuum control motor screws.
   1. Slide the rod out of the door and remove the panel/floor door vacuum control motor.

1. Remove the electronic actuator.
   1. Disconnect the electrical connector.
   1. Remove the three screws.
   1. Pull down to release the actuator shaft and remove the electronic actuator.

your problem is caused by the air temperature control blend door actuator motor being defective, the little motor moves the door that gives either hot air or cold air or a blend of the 2.