2003 Ford Explorer Heat

Please help, I purchased a 2003 Explorer V8 about 3 years ago and the heat was excelllent. Last week I turned the heater on and all I got was cool to very warm air. The engine temparature in fine (in the normal range). I have the digital controls and even when I turn it to 90 it still gives off very warm air. I checked the cooolant and it's fine. In my area you need to have an appointment 3 weeks in advance for them to look at your car, thanks!