Hi my name is John.
Does the blower motor come on at all?
That what blow the air.
When you turn on the heater does it blow any air out heater vents?
What size engine do you have?
Is this a 1500or 2500 pick up?
Do you have automatic air or manual?
I would check the fuse first.
Here a picture where it is under the hood.
It a 40 amp fuse.
Let me know.
If you have automatic air where you set the temp.
There a TSB that says to replace the blower motor control module for this problem.
But you didn't tell me if you have automatic air or manual?
I would remove the panel under the dash on the right side and disconnect the blower motor resistor connect and test for power at termial g,if there power i would replace the blower motor resistor.
You could also test to see if there power at the blower motor it self it right next to the resistor.If there power to the motor than the resistor is good.
Let me know
The easy way is with a test light.
You could take a light bulb and to wires hook one to ground and the other to the pin g in connector .It should light up.
Tail lamp bulb will work.