2000 Ford Expedition HEATER WONT BLOW HOT AIR, JUST LIKE A

Run the self diagnostic test on it by turning the key to on, then press off and floor at the same time, then within 2 secs, press auto, If there is a problem a trouble code will appear on the display...To exit self test, press the BLUE, cooler button this also retains error codes, To erase code and exit, press defrost, choose one of these before you power down the system... Test with engine at 120 degrees or more, and cabine between 40-90 degrees.Post any codes recorded here and I let you know what's defective...if 88 comes up, the system is OK but the core may need to be backflushed. Radiator shop can help out there.