Here's what I posted up a while back.... Since you have rear heat you can probably rule out a bad thermostat.
I had the same problem with no front heat.... and now it's fixed.... for free... Here's the steps I went through.
1) Replaced thermostat and changed anti-freeze. Figured it was time to change the anti-freeze anyway and a new thermostat always fixed my other
vehicles. Well... no change.
2) Opened up the glove box all the way (pull the tabs back at the top and fold it down) and felt under the dash near the heater core to see if I was getting heat there.... almost burnt my hand so I knew the core was not the problem.
3) Did some more internet research and found that the blend doors are a problem for fords (mostly F150 and Explorer) but figured that was the problem. Also found
this from another site that shows how to test the ATC unit.
By the way the DTC code that I got from running this test was 025, which is Intermittent Run - time Fault for hte Blend door actuator. You might also get a DTC code of 024, which is Self-Test Fault for the blend door actuator. If there is a fault a three digit number will be displayed where the temperature is usually displayed on the ATC. Good Luck
lThe EATC module self-test will not detect concerns associated with data link messages like engine coolant temperature or vehicle speed signals. A NGS tester must be used to retrieve these concerns.
The EATC module self-test will detect concerns in the system control functions and will display hard Diagnostic trouble codes (DTC) in addition to intermittent diagnostic trouble codes for concerns that occur during system operation. The vehicle interior temperature should be between 4ē-32ēC (40-90ēF) when performing the self-test. If the temperatures are not within the specified ranges, false in-car temperature sensor DTCs will be displayed.
The self-test can be initiated at any time. Normal operation of the system stops when the self-test is activated.
To enter the self-test, press the OFF and FLOOR buttons simultaneously and then press the AUTOMATIC button within two seconds. The display will show a pulse tracer going around the center of the display window. The test may run as long as 30 seconds. Record all DTCs displayed.
If any DTCs appear during the self-test, follow the diagnostics procedure given under ACTION for each DTC given.
If a condition exists but no DTCs appear during the self-test, refer to the Symptom Chart Condition: The EATC System Is Inoperative, Intermittent or Improper Operation.
To exit self-test and retain all intermittent DTCs, push the blue (cooler) button. The control will exit self-test, retain all intermittent diagnostic trouble codes and then turn OFF (display blank).
To exit self-test and clear all diagnostic trouble codes, press the DEFROST button. The vacuum fluorescent display window will show 888 and all function symbols for one second. Then, the EATC control assembly will turn OFF (display blank) and all DTCs will be cleared.
Always exit the self-test before powering the system down (system turned OFF).
Intermittent DTCs will be deleted after 80 ignition switch ON cycles after the intermittent condition occurs.
I got an error code of 22E and 66 (2003 limited).... not sure what they mean but I went on the hunch that the motor was shot (hoping it was not the control unit) and dug in to figure out if the blend door was indeed the problem.
4) Removed the panel in front of the heater core and you can reach around from the left side and verify that the door is all the way back. Mine was stuck there no matter where the control was set.
5) Unplugged the white plug going to the blend door actuator motor and reran self test. No Change.
6) Removed the actuator motor. I just pried it up off of the black tabs. Not to bad to do. Now I was about to go to
Ford and buy a new one figuring it was the problem but decided to pull it apart since I had nothing to lose.
7) To pull it apart there are about 8 tabs on the side. Nothing popped out when the cover came off and there are three gears in there. The white gear that drives the door has about 5 fingers on the back that run against the circuit board and the circuit board is just etch so I cleaned it off and put it back together.
8) Went out to the truck and plugged the motor back in and ran self test. The shaft turned and the error codes were gone.
Snapped the motor back in place, put the cover back on the heater core and I now have HEAT. Just in time as we got our first snow here in Steamboat a couple days ago.
Now if you want to check this I would suggest running the self test and if you get the same codes just open the glove box all the way and pop the actuator off. Take it apart and clean the contacts and then plug it back in and see if it clears the codes. If it does then you are back in business faster than it took me to type this up. Oh... and be thankful you don't have an Explorer... the doors tend to break on them and to replace it you have to pull the entire dash.
Hope this helps someone out.