I have a 1998 Ford Expedition 4X4, Everything was working last time I used it, but now I tried the Heater in all positions and I get nothing but cool air. I tried putting it back on Air Conditioning side and it switches. I really don't have much of an idea to where to start. Any Ideas???????????

 

First check the antifreeze level, if it's low the heater won't work. Also check that the engine temp guage is getting warm - around 220.

Marty

 

I had the same problem with my '01 Explorer and isolated it to the blend door actuator. From what I've read on this and related forums, blend door issues seem to be the #1 cause of loss of heat. Do a search on "blend door" and you'll see what I mean. If know your way around a car you can probably fix it yourself. Otherwise expect to spend upwards of $1000 to have someone fix it for you.