heater blows cold air only

I have check the heater hose coming from the engine and they are both hot. I guessing that it under the dash is my problem. Where should I look first. I am working on 1998 expedition

There is a good chance the blend door is broke. It's not uncommon for that age of vehicle. The F-150's have the same problem.

It requires disassembling the dash and duct work behind the dash. It's usually a bigger job than most people want to tackle.

Check your heater control knob and make sure it is actually turning the heater valve on the dash. Many of them crack and just spin on the shaft. Pliers will turn the shaft to see if it is working. Simple test. My 98 is like that right now. I need to replace the control knob. You will also see many others on the forum with the same problem.

Ordered the replacement knob from Ford today. $11.00.