My heater is not working - blows cold air?

The Blend door actuator is N/G. Many people have had the same problem for over 10 years. I am surprised Ford/Lincoln/Mercury have not corrected the problem.
The repair for this is $1000.00+
Ridiculous but true, I hear the whole dash needs to be removed.

If you are mechanically inclined and want to save a lot of money, there is a "Quick Fix" on this problem.
I will send you the link and you can take a peek if you are interested. Just let me know and I will send it right to you.
Sorry for the bad news;
Rick

Actually, you should be able to access the vent door from under the dash. You may have to remove the glove box.

NOTE: Because your vehicle has an airbag, I would recommend disconnecting the battery for at least 30 minutes prior to starting any repairs. Air bags can deploy if not handled correctly.

Dual Automatic Temperature Control Module On-demand Self-Test The DATC module on-demand self-test will retrieve on-demand (hard fault) DTCs only, it will not retrieve continuous DTCs. Continuous DTCs can be cleared when exiting the DATC module on-demand self-test. Make sure to retrieve continuous DTCs by carrying out the Dual Automatic Temperature Control Module - Retrieve Continuous DTCs procedure before clearing any continuous DTCs. � � � The DATC module on-demand self-test will not detect concerns associated with data link messages like engine coolant temperature or vehicle speed signals. A diagnostic tool must be used to retrieve these concerns. � � � The DATC module on-demand self-test will detect concerns in the system control functions and will display on-demand (hard fault) DTCs for concerns that are present during the self-test. The vehicle interior temperature should be between 4 °C - 38 °C (40 °F - 100 °F) when performing the self-test. If the temperatures are not within the specified ranges, false DTCs may be displayed. � � � The self-test can be initiated after cycling the ignition switch from OFF to ON. Normal operation of the climate control system stops when the self-test is activated. � � � To enter the self-test press the OFF and FLOOR buttons simultaneously and release, then press the AUTO button within two seconds. The display will show a flashing blower icon for 20 seconds, after which all vacuum fluorescent segments will be displayed if there are no on-demand DTCs present. If DTCs are present the DATC module will display "00 00" and then on-demand DTCs. Record all DTCs displayed. � � � If any DTCs appear during the self-test, carry out the diagnostic procedure. Refer to the DIAGNOSTIC TROUBLE CODE INDEX and follow the ACTION for each DTC given. � � � If a condition exists but no DTCs appear during the self-test, GO to Symptom Chart Condition: The DATC System Is Inoperative, Intermittent or Incorrect Operation. � � � To exit the self-test and retain all continuous DTCs, press any button except DEFROST. The DATC module will exit the self -test and retain all continuous DTCs. � � � To exit the self-test and clear all continuous DTCs, press the DEFROST button. The DATC module will exit the self-test and all continuous DTCs will be cleared. � � � Always exit the self -test before powering the system down (system turned OFF). Once the self- test is exited the ignition switch must remain ON for at least 30 seconds to allow the temperature blend door actuators to automatically recalibrate. � � � Continuous DTCs will be deleted after 80 ignition switch ON cycles after the intermittent fault occurs.
3/28/2009

Sounds like the blend door actuator inside the dash. This is common with most Ford truck models for several years now.

Heater Core "” Plugged

WARNING: The heater core inlet hose will become too hot to handle if the system is working correctly.

Check to see that the engine coolant is at the correct level.
Start the engine and turn on the heater.
When the engine coolant reaches operating temperature, feel the heater core inlet and outlet hose to see if they are hot.
If the inlet hose is not hot:

the thermostat is not working correctly.
If the outlet hose is not hot:

the heater core may have an air pocket.
The heater core may be restricted or plugged.
If both are hot, the temperature blend door in the heater plenum may be broken or stuck.
Is it auto temp control? Or manual?

Unfortunately you very possibly could be another Explorer/Mountaineer owner with a Blend Door Actuator problem.
The repair is BIG $$ ..$1000+ ...and that is no B.S.
A large portion for the repair is labor.
The whole dash needs to be removed. This problem has been going on fo 10+ years and Ford/Lincoln/Mercury has not done on thing to correct the faulty plastic pivot arm.
There "is" a quick fix for it if you can do it yourself and save a lot of money.

Sorry to be the one to give you the bad news.
Here is the link for the quick fix.. it was done on a 1996 but they are all the same. Check out what it states in step: 9 about how much you saved!

https://www.2carpros.com/topics/climate-control/blend-door

Good Luck;
Rick

Is the engine running at operating temp
if so
Check heater hoses at the fire wall
if both are hot
suspect blend door in the HVAC box
usually you hear clicking in under the dash

To fix the problem locate the blend door, and spray WD-40 on the pivot points.