No heat in 98' Dodge ram

many times the 1 way valve on the passenger side of the intake where the HVAC lines come out go bad. The line comes out about half way back and down low on the side of the intake. check to see if you get hot air thru the defroster...also could be the line from the intake that runs thru the firewall to the vacuum control of the heater/mixer door or vent- defrost door is busted. The easiest place to start is at the 1 way valve, this will typically cause the air to default to the defroster when the engine is under load.