I am having the same problem. The dealer wants to charge 100.00 to fix the one post which isn't horrible but I would rather have metal parts so that it doesn't happen again. Do you know what the site is for the aftermarket kit?
heater core going bad.
HEATER CORE.
could possibly be the blower motor resistor. which is generally located on the passenger side under the dashboard by the blower motor.
The expedition door lock relay could be stuck causing the grinding noise. Check to insure that the lock relay is working properly.
sounds like your heater core went out
the heater core is in the dashboard on the passenger side. if you dont work on cars alot you may want to just pay a mechanic, taking apart an old brittle dashboard can be a headache. You could also check the library computers for an automotive program that gives you detailed pictures or step by step procedure.
Thermostat.....
There's a good chance that your heater core has sprung a leak.
This could either be due to the age or the materials used to make the water heater or the fact that the water heater has not been installed with vacuum breakers causing the geyser to collapse from the inside-out due to incorrect atmospheric pressure within the water heater
Check you heater blower motor. This sounds more like the common blend door problem on this model. The plastic door is driven by a DC motor that is geared too strong for the application. Over time the motor will overstress the door and break the connector. The same plenum box is used on the F150 and you can find information on the problem by searching for that model also. There is a video available on YouTube showing how to diagnose and repair the system. It is an expensive repair at the dealer, but you can repair it yourself with minimal skills. You can follow links on my bio page for pictures and additional information on how to diagnose and repair the problem.
If it is water, it could be a plugged up AC condensation drain or if it is engine coolant, it could be a leaky heater core.
could be fans not working, thermostat, blown head gasket, broken or leaking coolant lines, bad heater core