Cold air from the defrost indicates that the air doors are in the wrong position. The doors are vacuum controlled in most vehicles. check the vacuum system for a leak.
There may be several reasons why the air only blows out the front vents and not on the floor or the defrost on the 2003 Dodge Ram. The fuses may be blown, or the heating coil is not working correctly.
Most likely a bad or disconnected vacuum hose to the defrost/floor selector in the heater ducting.
the heat blows out the defrost when it should blow out floor vents only
You lost the vacuume supply coming from the engine, defrost is the default mode if a mafunction in the vacuume supply is lost.
The 1984 Buick uses vacuum lines to change air flow from defroster to ac vents. Check the entire vacuum system for leaks.
If it smells musty check the evaporator drain hose hose. Johnny Texas.
This is the same on all cars. When the air flow is OFF in a section, the it blows stronger to the other vents. In this case the ones for the windshield. This makes defrosting quicker so you can start driving safely sooner.
The first thing that you need to check will be the vacuum hoses for leaks, breaks or loose fitting ones.....
why dont bottom vent doors not open on 2001 gmcsonoma
most vehicles use a vacuum diaphragm to move the mode door inside the dash from the floor to the vents to the windshield. Either the vacuum diaphragm is leaking or the vacuum hose has become disconnected. In my 85 topaz the door pannel vents are used to defrost the side windows.
The doors are electric. You most likely have a broken door inside the heater box under the dash.
Grand Marquis are designed and wired so that the VAC door fails and will even cause engine not to start due to wires be connected together under dash.