Heater doesn't blow hot air

2009 Mercury Mountaineer, my heater wont work unless I'm driving and get over 50 mph... I let my car warm up for 20-30 minutes and it wont defrost my windshield, it only blows cold air.

Souds like it's way low on coolant. The heater will blow cold air when the cooling system is so low that there is no water (coolant) running through the heater core. Then the thermostat opens, it trys to be normal but the system is low so it gets too hot in just a few minutes. If its that low, there must be a leak somwhere.

you might want to check the module under the glovebox

Try flushing or blowing high pressure air through the heater core lines. its sludge build up and need to be flushed through heater core only. check antifreeze fluid level. only put in straight antifreeze, do not mix. most people do not know what mixture should be, so be safe and add straight, it will not hurt it, i run 100% straight antifreeze and never had a problem or worry about it ever freezing and cracking my block, heads or radiator cracking.

I had a similar problem with my 2003 intrepid. The problem turned out to be the control panel. I went to a salvage yard and got one.

You likely have low coolant causing a large air pocket. This will cause the sensor to pick up the hot steam but the lack of flow through the heater core will not heat up the interior.

You likely have a restriction in the heater coolant hose circuit - perhaps a coolant control valve not fully opening, or a kinked hose.
Insufficient coolant volume is flowing to keep the heater core hot.
Try back flushing the heater core system with a garden hose to check flow.

sounds like a weak waterpump or low level

Does the car run cold or is the temp. correct. Check the thermostat first. check that the radiator and res. is full. Check the hoses to and from the heater core. If one is hot and one is cold then either the shut-off valve to the heater core is defective or the heater core is plugged.

I have a 96 Intrepid, and none of the signal lights work. I tried replacing the fuse, but this did not remedy the problem. Could this be a loose connection?