heater is not working on my f350

Is the fan not working or is the heater not blowing heat? if fan is not blowing check switch and blower motor. If its not blowing heat, check heater core

1994 f350 diesel dually Fan works, new heater core Why No heat in cabin ?

How is your temperature gauge reading? Does it get hot? If not, your thermostat might be stuck open, flowing coolant to the radiator before it is warmed enough. If it is normal, than there may be a restriction in the lines to the heater core. If all checks out well, your blend door may not be opening. I cant recall if its a blend door setup, or a valve on the heater core inlet. If its not a blend door, then your heater control valve might have a broken line.

temp gauge is fine, fluid level is good, just no heat blows

heater does not come on blower until i start driving then it blows fine

Fan has not blow on high(burst of air) for years) all of a sudden fan quit blowing one day. Ac pump icks on . One day it might blow. But probley no going to. I put new fan motor on a. Year ago. ???

Check the fuses. There's a blower resistor ($20) in the engine bay usually near the blower motor or where the A/C lines go into black box. If this works it's an easy fix. Usually one of fan speeds will stop working and maybe another before it stops completely. Fan motor ($50). I'm sure by now you know I'm not auto technician. Check the switches on the dash.