blend door fix

1996-2007 Ford Taurus Mercury Sable - Heat and AC Blend Door Replacement Parts

  This is a product developed by the HeaterTreater Engineers for the common blend door failure problem on the 96-07 Taurus and Sable(same car, different names). Please check our feedback to get an idea of the product line integrity and customer reaction to our products. We are committed to customer satisfaction and successful repairs of blend door problems. 

This is a kit to do a complete repair on the blend door malfunction that is common to the 96-2007 Ford Taurus.   Every Taurus in this range either has, or will have, this common failure.  The pictures show the hardware provided for the fix.  All work is done through the glove compartment removal of the dash panel or evacuating the AC system and draining the radiator.  Once completed, the alterations are behind the glove box and are not visible.  The work to install the fix is relatively simple and can be accomplished by the average shade tree mechanic. The work could easily be done by any local independent garage. Product returns are accepted within two weeks for a full refund(minus shipping).

The standard fix for the blend door failure is to remove the heater box and replace the plastic door. If the instructions with the door start out with "remove the heater box" �be ready for considerable work. Removal of the box requires removing the steering wheel and steering column, dash panel, console, evacuating and disconnecting the AC compressor, draining and disconnecting the heater hoses. Fixing the door is relatively easy, but the labor(and cost) of getting to the door makes this a time consuming and expensive job. The HeaterTreater avoids the hard work by providing a kit that allows the repair to be done with superior components without having to disassemble the automobile. 30min work vs 8-14 hrs of work, and no specialized mechanical skills required(or EPA certification to evacuate and recharge the AC).


The Problem:

-  The Taurus is built with a Blend Door to control the heater and AC function.  On the Taurus, air flows through the AC evaporator which can be switched either off or on.  The blend door can then divert air through the heater core or directly into the vent system.  By positioning the door to regulate the amount of air going through the heater core, temperature can be regulated with good accuracy. 

The doors are controlled by a DC motor capable of moving the door in both directions. The issue with the system is that the system has to calibrate itself and find the end points of movement before the computer can understand the two closed positions and regulate the temperature.  The computer drives the motor until it stalls, creating significant force on the plastic door and axle.  The photograph shows the fail mode on the Taurus.  Over time the plastic door cannot withstand the rotational force from the motor and the axle breaks.  More detailed information on the general operation of HVAC systems is available on our web site at

Do you have the problem?

The usual symptom is an inability to effectively control the temperature of the HVAC system. The door rotates on a horizontal axis and when the door breaks, it falls to the bottom of the box, blocking the heater core.  This means that very little air can flow through the heater core and the primary effect is loss of heat.  Also, since the door is just laying there, it does not give a complete seal and AC efficiency will suffer.   While these symptoms are fairly conclusive for blend door failure, the only way to really check it out is to remove the blend door actuator motor and look at the axle.  The picture shows a view through a fully opened glove box(squeeze the sides of the box and pull out).  The white plastic motor is visible and can be removed by loosening two screws and pulling the motor straight back from the heater box.  The motor is covered by a metal covering to protect the components during the the factory assembly.  This cover is held on by two screws that also have to be removed.   You can use a mirror to look at the axle or check by feel.  If the axle looks/feels like the picture of the broken blend door, this is conclusively your problem and the HeaterTreater will fix it.

Note also that a blocked heater core is a common failure on the Taurus.  The picture shows where the heater hoses go into the firewall in the engine compartment.  You can remove these two hoses and use a water hose connector to connect a section of hose and flush the heater core.  If there is no, or diminished, flow through the heater core, this will affect heater operation. 

Another reported fail symptom is a “clicking� sound coming from behind the glove box. This occurs when the motor gears get out of alignment and are slipping against each other, making the noise. Sometimes you can make it stop by pushing down on the back of the motor and getting the gears to catch. This occurs during the calibration cycle described above and the motor will continue to run until it hits the stall point which never occurs if the gears are slipping. The clicking will cause permanent damage to the motor, stripping the gears. The failure usually occurs with a broken blend door that allows the motor to get out of alignment and twist slightly, causing the gears to disengage. The HeaterTreater will put the system back in alignment and correct this problem.

The HeaterTreater TM Solution:

This kit replaces the plastic doors and axle with stainless steel components.  All work is done through the glove box opening and no disassembly of the dash or evacuation of the AC system is required.  Tools required are a screw driver, and a rotary cutter(Dremel tool)( if you don't already have one, this is a good excuse and the tool has many uses. The opening through the glove box is confined and you will need a flexible extension for the rotary tool. Target has a very good tool from DuraBuilt that has the flexible extension for less than 30 bucks ).  Correct cutting bit, and all hardware is provided. 

Of all the blend door replacement kits that we have developed, installation on the Taurus is the easiest.  The repair will take about half an hour.  No extensive mechanical skills are required.  The picture shows the metal replacement kit.  The plastic door is accessed by using the Dremel tool and bit to cut into the plastic heater housing through the glove box.  Complete diagrams for the cutting pattern are provided.  It's a very simple process.  The broken plastic door is removed and replaced with the
HeaterTreater TM

The instructions are written with multiple pictures and dual level instructions.  You can read the bold print only for experienced mechanics or read the bold and standard for full "instructions for Dummies".  The instructions are almost insultingly simplistic for those who care to read the entire document without admitting that they did it.  The fix is easy and MUCH preferable to disassembly of the entire dash and engine cooling systems(or paying the dealer to do it for $600-$1100). We provide support via email or phone if required. Our goal is to make sure that every installation is successful. To date we have achieved that goal and have no intention of letting up. This will solve the problems with the blend door and is over-engineered to outlast the Ranger.


Tech Talk for those that are interested.

While installation of the door is easy, construction of the hardware is not.  Note in the picture of the broken door that the side of the door is wedge shaped.  The fully closed position on either extent takes this angle into account.  Most systems use a flat door centered on the axle and are easier to construct.  One position seals the heater core for max AC operation and the other extent forces all air through the heater core.  With the wedge shaped door, you can't center the door on the axle without having minor leaks in both directions, and constructing a wedge shaped door adds weight to the door and manufacturing complexity(cost) to the product. 

The HVAC system has two sources of temperature control, the heater core and the AC evaporator.  Heat from the engine is "free" and hot(upwards of 200 degrees).  AC, however, takes additional work from the engine and the system is only capable of producing a set differential from ambient.  The HeaterTreater door is constructed to bias toward maximum AC efficiency for the reasons above.  Note in the picture that there is a double thickness of foam on one side of the door.  This does an acceptable job of sealing the vent system and forcing all air through the heater core, but is not perfect.  Since most humans are not comfortable at 200 degrees, we generally run the heater full blast to get the car warmed up on a cold day and then adjust the temperature down.   Once the engine reaches operating temperature, there is no issue, but as the water in the system is heating, you are trying to squeeze out every degree on the way up.  This process will be less efficient and the impact will be an extra 30sec to 1min to get the car warmed up on a cold day. 

In the picture of the broken door, you can see a lever that is connected to the axle.  This controls a backside flap that closes off the heater core in full AC mode.  Air can take two paths through the system.  One directly into the vent system and the other through the heater core and into the vent system.  Think of the heater core as a side road that can be taken when it's cold.  When air flow is blocked through the heater core, the back side of the tunnel is still open to the vent system and even without air flow, there is some radiant heat that can warm the air in the vent system.  The Taurus has a flap that blocks radiant heat during full AC mode.  The little lever is connected to a slide control arm and spring to control this back side door.  It is way over-engineered compared to other automotive systems and adds considerable complexity to replacing the blend door.  With the HeaterTreater, this Rube Goldberg system is replaced with a simple counterweight that will hold the door closed, and open when air flowing through the heater core pushes the door open.  Simple and 100% effective.  This requires a little more air flow to open the door, but that is done by raising the temperature slightly.  The system will operate the same as before, but the desired temperature setting may have to be adjusted slightly upwards to get the same results as before.   There is no compromise to full AC performance or full heater performance.  The only variation will be when you are running the AC and it's too cold and you want to add a little heat.  You will need to set the temperature a little higher to force a little more air into the heater core to provide enough flow to crack the counterweighted door open.  You still have full control over temperature.


All HeaterTreater products are designed and tested for reliability by degreed professional engineers.  We strive for 100% customer satisfaction and have maintained that objective to date.  We have no intention of backing off of that accomplishment. 


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