Hello:

I have a 1999 Expedition which I love dearly. Best vehicle I ever owned. However, the heater has just started acting funny. The front heater will not blow hot air, no matter how I set the temperature. The A/C works fine, but the heater in front blows cold air. Defroster is cold only too. The rear heater works fine. No problem. I purchased a shop manual, but can't for the life of me figure out what's wrong. How can one heater work and not the other ?

I read somewhere that it might be a problem with my "Blend Door". What the hell is a blend door and where on the vehicle can I find it ?

 

The blend door is in the Heater A/C plenum. It's function is a 'flow gate' for heat and A/C temp control.. It's driven with a blend door motor..

Here's a couple of images of the blend door.. One in the 'OFF' position and the other showing HEAT/ Blower 'flow' through the heater core..

[IMG]local://upfiles/6756/CE0DC22DCB18492BB72E16556CCAA1B3.gif[/IMG]

[IMG]local://upfiles/6756/B0CD94D576044C24A629F9317A2E51D9.gif[/IMG]

 

Great info. I see how it works. Where exactly is it located though. Is it something I can get to and try to work on, or is this a dealership issue ?

 

The Plenum Chamber is located 'behind' the intrument panel, and behind the glove box area on over to about the center of the dash.. If you have a no heat issue it should be diagnosed as to the cause prior to any dash work if possible.. If a bad blend door, or door actuator/motor is the cause, then it's a 'sizeable' job to complete..