I have done some more research and now believe that the "Blend Door" is either stuck or broken. Most likely it is broken because I have performed the self test diagnostic posted and everything checks OK electrically/vacuum (readout of "888").
From a .jpg posted by "SVT2B", I believe that the blend door is located between the defrost/panel actuator door and the A/C condensor and just in front of where the heater core is located pictured here:

Blend Door image



If I am incorrect in my assumptions please let me know. I have contacted two(2) of my local Ford dealerships and they both say that the heater box would cost $216.00USD and they want around $400-$480USD for 8 hours labor. OUCH! That's a total of $696.00USD plus tax. If someone knows of the best way to replace/fix this door please let me know.

Thanks again

 

Good Luck.It's ashame that this is happening so much and FORD will not do any thing about it .Mine is on a 97 Ranger .I have talked to Ford reps till a can't know more.They frist talked like they were going to help if I had the Dealer tell them what is wrong.Crazy me I go to the dealer (for $45.00) to get told that is the blend door . You have to replace the whole blend door assembly for another $ 800.00 .The rep calls my dealer and then she calls me back to say she's sorry they can't help.So good luck, I epoxy the door to the door motor and it 's been doing alright so far

 

OK, where do I start? As stated earlier, I took the vehicle to the local dealership and they ran a compter check on the system with no codes. They stated that the "Blend Door" was possibly broken. I believe that for this reasoning is that since the "Blend Door" was broken there was no codes, the actuator motor that controls the door was actually working and not giving a code. Yet, since it was broken everything seemed to be working correctly according to the diagnostics. Luckily I made friends with a local body shop owner and he also has the proper equipment to verify what the local dealership stated. I swapped some computer work for him fixing my delima. We ordered a replacement (new) evaporator box from "Ford" and removed the entire dash area except for the steering wheel and column. We even removed the front two seats, and center console. After removing the old evaporator box, which involved purging the A/C, and drainin the coolant, we opened the box and WALA! the blend door was broken. It was broken at the bottom where it attaches to the actuator motor. We reinstalled the evaporator, heater core, etc. and all other associated pieces and reinstalled the dash and everything worked perfectly. I just hope that there was some sort of engineering change on this new box that will prevent this from happening again.

 

Hey guys,
I know this is a late response but this question came up first on google so I thought I'd help out others visiting...The blend door problem now has a fast and relatively simple solution. It is called the Heatertreater kit and it doesn't require removal of the dash or an expensive shop fix. Check out heatertreater.net for full diagnostic info and the kit.

 

I also heard about Heater Treater from the show "TruckU" a few weeks ago. Looks like the way to go:
http://www.heatertreater.net/

 

HOLY CRAP, this was an 8-year old thread. Well, I hope someone can use this info...

 

I to bought an 03' with a blend door problem but refused to accept the magnitude of replacing it. So I continued to check and recheck everything. My reason was that I thought I should be getting better than 15 MPG from my 5.4.
Upon checking I found a vacuum line alongside the front passenger tire with a broken fitting, thinking I found the problem, wrong.
Well after continuing to check vacuum I discovered the vacuum at the control motor was not there, I ran a temporary line to the control switch and wha lah! it worked. I spliced into a constant vac line under the hood on the passenger side and ran the new line across and through the loom that is at the top of the firewall and routed it through the firewall near the steering column and up to the switch. Less than 5.00 in parts and about 45 minutes ( after several hours of looking) and it has worked since with no problems.

Somewhere under the dash the line is broken and I'm not sure where nor do I care. Nobody would ever know that there is a new line.
Now my MPG are a decent 17.2 hi-way, 70 MPH and regularly and trying to get to 18.