1998 ford f 150 the heater doesnt work.It blows cold air instead of hot on 1998 Ford F-150

cold instead of hot and kind of warm when turned to aircondision.Blend door is fine coolant is fine thermostat is fine.What is wrong?

Asked by for the 1998 Ford F-150
low coolant level, thermostat not working, air in system, clogged heater core and bad blend door motor are causes for this.

we checked blend door and flushed heater core it has a new thermostat and plenty of coolant.We seem to have checked all the normal things that cause this problem.Still defrost gives cold air and a/c side on pannel gets warm.Is there anything else any one can think of?
do both hoses feel hot or is 1 hot and 1 cold?