Metal nails are hammered into two (or more) pieces of wood to fix them together.
This sounds like a Blend Door problem. The problem is that the blend door in the plenum is stuck in the A/C position and will not reposition to allow heat. There are two possible issues. 1: The Acuator has snapped off (plastic breaks) 2: The Blend Door is broken (plastic hinge broke) There are related articles to fix both of these conditions
The blend door and recirculation door..
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The blend door regulates heat and AC in today's automobiles. Generally the system is set up with air always flowing through the AC evaporator coils, and the compressor is either on or off, cooling or neutral under system control. Now the air flowing through the evaporator is either directed into the vent system, or directed through the heater core and into the vent system. The blend door regulates the amount of air that is allowed to go through the heater core. For AC, the compressor is on and the blend door blocks air flow through the heater core. For heat, the compressor is off and the blend door diverts air through the heater core. Those are the two extremes, and exacting temperature control is achieved by having the blend door in intermediate positions between the two extremes. Remember the slide bar on the AC control panel on older cars? That slide lever was connected by cable to the blend door and temperature control was achieved by sliding the lever. On modern automobiles, that function has been transferred to computer control, using a pseudo stepper motor to control the blend door. On late 90 and early 00 cars, the motor was connected to the same plastic blend doors that were used with the slide scenario and there is a recurring problem over time with the motor being too strong and breaking the plastic blend door, leaving no control over temperature. The fix is to remove the heater box, which is a very involved operation, and replace the plastic door(which WILL break again over time). Additional information on the cause and a cheap easy solution is available at HeaterTreater at www.heatertreater.net, or follow the Google ads on this forum. cgallen
The actuator motor is on the front side of the plenum box and can be seen through the glove box opening by fully opening the glove box and looking to the left. The motor is held in place with two Phillips screws and is fairly easy to remove. The most common fail is not the motor, but a broken blend door. Check this web site for diagnostic information and a fix. heatertreater.net.
The most common problem with this system is a broken connector to the blend door. The blend door and axle are metal and the motor drive connector is metal, but in a fit of brilliance Dodge elected to connect these two components together with a plastic connector. When the plastic breaks, the motor will turn past the point where the electronics can sense the position of the door and the motor will appear to be non-functional because the computer shuts it down. An aftermarket replacement for the connector is available. Additional information can be found by going to my bio page.
Your system has 2 "blend doors". They blend the hot/cold air for the right temperature. For whatever reason, one of your blend doors is not operating properly. Two likely possibilities: 1. The hinge on the blend door is broken so the door can't move 2. The actuator that powers the door is shot 3. (least likely) Your control unit (or wiring) is faulty. A dealer repair on this may be spendy. To get to the blend door they need to drop the steering column and remove the entire dash.
There are two Blend Door motors. One each on the left and right side of the heater box located in the center of the dash. If one side is blowing hot air, it probably has a broken gear in the motor on that side.
You have to take the dash cover off. The blend door cable and swing arm are just under and in font of the defroster vent. You have to pretty much take the defroster vent out to access the cable and swing arm. This whole process will take a while as you have to take the center console out, the dash cover off, the passenger airbag out, and the dash off just to be able to actually work on the blend door. But take the top dash cover off and look under the defroster vent and you will see two cables one is the position cable and one is the temp cable (connected to the swing arm on the blend door. You will then get an idea of how much you need to take apart to fix the problem. It also depends on how small your hands are and if you can work on the problem without removing everything else.
The Expedition uses the same heater box as the F150 and Lincoln Navigator. The blend door acutator motor is located on the bottom of the box and the blend door turns on a vertical axis. The most common failure for these cars is for the plastic connection on the blend door to motor to break. It is very common to remove the blend door motor and have a handful of black plastic pieces fall out. This is a sure diagnostic of a broken blend door. The motor on the Expedition is located above the transmission tunnel. To get to the motor you will have to remove the center console. You will see a black plastic vent under the box. This is for air distribution to the passenger and drivers side floor boards. The acutator is just above this vent and the vent has to be removed to get to it. The Expedition was not designed for repairing this problem and the Dealer process is to remove the steering wheel, steering collumn, complete dash panel, evacuate the AC, drain the radiator, and finally remove the heater box to get to the actuator and blend door. For us cheap guys, the bottom vent can be removed with enough force and creativity. You may have to cut it with a dremel tool to remove it. This is not a structural or high pressure vent, so it can easily be repaired with metal duct tape and is completely hidden when you replace it. You can also reconnect the motor and see if it is working properly. Once you get the the motor, it is easy to remove the screws and pull it straight down. Look for broken pieces and/or examine the connector with a mirror for signs of cracks. You can manually turn the blend door with a flat piece of bent metal and switch from AC to heat to see if the door is working properly or hanging. If the door is broken, you have two options. Take it to the dealer and have them go through the process above and replace the door with another plastic door that will also break over time, or check the HeaterTreater fix on Ebay. This replaces the door with metal and the fix is done through the glove box opening without the 12hrs labor to remove the dash.