low heat on 1996 Ford E-150

warm not hot air coming from heater

2 answers
flush heater core take heater hose off at engine get couplen to go in heater hose then take water flush one hose then the other till water runs clear ,you may have to change therostat use 195deg
If the heater engine is at proper operating temperature, however, you could have an issue in the dash with the part that changes hot air to cold.