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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
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Are the blend air door air or electrically operated on 1998 Ford Taurus?
the blend door is operated by the blend door actuator motor which is electric.Fairly easy fix too...See "Related Questions" below for more
Why does the blend door actuator make the clicking noise?
Probibly your blend door motor is stripped out. Remove motor and check door operation manually
How do you replace blend door actuator on 97 ford expedition?
How do i replace blend door motor
Why does BMW 2001 325i ac blows warm air?
if the compressor is running and it is still blowing hot air i would have to say that the blend door is not operating properly. if the blend door is stuck open then the air is still blowing across the heater core and into the cabin. replacing the motor that controls the blend door will most likely fix this problem
Y does the rear ac make a poping sound when its on?
rear blend door motor is bad rear blend door actuator motor is bad
Where is the blend door on a 2003 Nissan Altima?
The air mix door electric motor is located drivers side. must remove drivers lower instrument panel. door motor is located to the right side on the airbox assembly
How do you replace blend door actuator motor on 1999 ranger?
how to replace a blend door actuator on a 1999 ford ranger
Why is the heat not working on your 5.3L 1999 silverrado Pickup 4x4?
Sounds like your blend door may be broken. the blend door opens and closes on the heater core to allow heat into the cab by letting the air blow over the heater core. The heater core basically looks like a small radiator and when the blend door gets opened up, it allows to air from the blower motor to blow through the heater core fins and that heats the air before it is pushed out the vents into the cab... Check out www.heatertreater.net Those guys have videos on there of what I am talking about. It may not be your blend door though. Could also be the blend door motor or the dial to turn from cold to hot... I would check that blend door first though...
How do you replace a blend air door on a 2000 Pontiac Bonneville?
how do you replace a blend air door assembly on a 2000 pontiac bonneville
Heater blend door motor location buick park avenue98?
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.
What does a air temperature control blend door actuator motor cost?
Temperature blend actuator motors price around $45-80.Lots of after-market alternatives to the Ford dealership.
Your front heater does not get hot but the rear works just fine on your 1998 Expedition?
Does your blower motor work? If it does and there is no heat the blend door actuator is probably not working and is not letting warm air into the vehicle. The blend door is staying in the cold position.
