Check the diverter valve under the hood.They are usually vaccum operated so check to see if you are getting vaccum on the line when the heat is turned on.If you have vaccum try taking the valve out and splicing the lines together.If that gets you heat head to the parts store,they are usually cheap to replace.
does it have ac or not no ac its not a heater control valve doesnt have one let vehicle run when its at running temp grab the heater hose outside the fire wall and see if they are both hot should be close on temp on both if one is hot and other is not clogged heater core both hot and no heat your flap in the heater box is stuck or cable has came un hooked double check this and find out now if ac is there see if the hoses are hot again if not apply vacume to heater control vavle if it fixes it find vacume leak no leak start looking into control switch or stuck flap doors again hope i can help you some with this
is the inside of your truck getting wet on the floor boards?? or is the truck getting very hot. if neither of those then see if leaking outside in the engine compartment and that no hoses are pinched. it could be heater core or something really basic. it maybe something i haven't even thought of
