Steam Cabins My Heater On My 2002 Ford Expedition Blows Warm For About 15 Seconds And Goes Cold, How Can I Fix It?

My heater on my 2002 Ford Expedition blows warm for about 15 seconds and goes cold, how can I fix it? - steam cabins

I have the selector and temperature control of the car, there is a real control of the head and the problem continues. I have no problem of leakage of coolant, no exhaust steam, great time on teaching.