2003 Mercury Mountaineer damper open/close but no hot air. There is heat but the damper is not openig.

the air from the blower will be the same temperature as the coolant temperature. If you want it hotter you may have to get a thermostat that opens at a higher temperature or close the air circulation vent so that only cabin air is heated.and not fresh freezing cold air from outside.

Unfortunately you are going to have to remove the dash to fix this problem. What has happened can be one of two things. The first is the ductwork has become unattached leading to the top vents. The second possibility is a damper is not working. With the engine off and the switch on, put the selector to defrost while listening closely. You should hear dampers opening and closing. If you don't, that may be the problem. They are either electrically controlled or operate off of vacuum. Hope this helps

This could be due to a failed blendoor actuator.

The Engine Temp. sensor is bad. it is under the intake manifold. if there is a miss also check under the coils over the spark plugs. If there is Coolant in the spark plug holes .then the intake gasket is leaking. The intake manifold needs to come off to change the coolant sensor. When off look for corrosion on the cylinder head at the coolant port. If there is corrsion then the cylinder head must be replaced.

there is a blend door motor that control the hot to cold,and it sounds to be stuck open or close.

there is a vacuum ran valve on your heater hoses goin in to your heater core on the fire wall, they tend to get stuck shut n dont open to let hot anti freeze in the heater core, so cold air right, qwik fix is find the valve on heater core inlet and wire tie it open so antifreeze circulates no matter what, this is known on ford explorers. pretty much same truck.

2004 mercury mountaineer.heat problem
When turning ac knob to heat clicking sound like door opening and closing repeatedly sounds and air blows cold instead of hot.

could be the temp blend motor not working. does the heat go from hot to cold or is the temp always the same?

no you have to remove the vent between the hood and the windsheild its on the out side of the car it sounds like your freshair vent is stuck open

You can't even reach the door without pulling the dash assembly out, then u might as well fix the problem,