Heater not working

What is it doing, blowing just cold air?

If it is you could possibly have a blend door actuator problem.
The actuator is not moving the door in the direction it needs to go to receive the hot air from the heater core.
It is a very popular problem with Explorers and Mountaineers. I am surprised that through the years Ford/Lincoln/Mercury has not corrected the issue.
Rick

Yep... the whole dash needs to be removed, $1000+ mainly for labor.
It has been going on for 10+ years and Ford/Lincoln/Mercury has not improved the design ....the S.O.B.'s
Here is the link for the quick fix if you want to do it yourself:

https://www.2carpros.com/articles/mitchell1eautorepair-car-repair-manuals

There "is" another way and that is cutting a hole near the heater core and using duct tape to seal it back up after the repair is done. I will see if I can track that one down and post it here.

THE HOLE WILL NOT CAUSE ANY PROBLEMS AT ALL

Good Luck;
Rick

Hey JGAULIEN,

There is a blower motor speed controller that has probably gone out, here is a wiring diagram and guide so you can do some testing.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

and

https://www.2carpros.com/articles/car-heater-not-working

Please run some tests and get back to us so we can continue helping you.

Best, Ken

Good afternoon.

That is the blend door actuator and the reason you have no heat. You need to replace the blend door actuator.

The procedure is below with pictures.

Roy

REMOVAL
1. Remove the floor console.
2. Remove the steering column opening cover.

ImageOpen In New TabZoom/Print

3. Remove the components in the order indicated in the illustration and table.

INSTALLATION
1. To install, reverse the removal procedure.

Check for a vacuum leak at heater. It may be at control or at vacuum motor or a bad vacuum motor. See picture. If the motor has to be removed the dash has to come out.

Are you sure the coolant is full?

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If not too hot to hold, then you have to look at the actual engine temp and if that is up, if it is, then your looking at a restricted heater core.
If you find that they are both too hot to hold, then the heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.
If they are both not too hot to hold on to, then you either have a restricted heater core or the system is not completely full and getting air pockets for some reason.

It's probably the actuator is broken or not moivng the piece inside the heater box. You'll have to check to see if it's working. If the actuator works then tehheater box has to be torn apart to fix the broken vent piece. Chek c number 1 on chart.

As a 1st step you need to start with the thermostat
check it and check its operation
if in doubt replace it