The Blower resistor should be tested which is located near the blower motor, the resistor is probably faulty.
On the B250 van the blower resistor is located behind the passenger glove box, remove the glove box shell and resistor is located just to the right side, you can't miss it.
The blower motor resistor is located under the hood, in the right hand cowl, behind the windshield washer bottle.............
I have been working on an issue with my 2002 Dodge Ram. The blower motor and resistor are both located on passenger side under the dash. Easily accessible in cab.
Under the cowl where the wipers are. Remove that and two screws to pull resistor out.
It's behind the glove box door
Under the dash, on the passenger side.
It is behind the glove box door.
Under the dash, far passenger side.
The blower motor resistor is located on the lower right side of the HVAC unit housing inside the the vehicle under the dash on the passengers side........
Your truck has both. the resistor is between the switch & blower.thje resistor controls the blower speed
Blower motor resistor assembly is located under dash board on passenger side.