Heating AC and Engine Cooling
Ford Taurus

How do you diagnose and fix heater blend door problems on a Ford Taurus - Mercury Sable?

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2015-07-15 20:44:15
2015-07-15 20:44:15

No. It is operated by an electric motor. But your problem may not be limited to the temp blend door motor. We also had problems with something in the heater box called a secondary stratification door. It works together with the blend door itself. Sometimes it would get warped and start hanging up. The solution is to replace the door with a revised door. It is also possible that you have an electrical problem in the heater blend door motor control circuit.

Mix door

The air mix door is malfunctioning or the controls are disconnected and allowing too much outside air to enter the cab. Sometimes you can get at the controls from the outside of the heater but you may have to open the heater to repair the mix door. Many times when cores are replaced the person forgets to reconnect the mix controls or breaks the connection unwittingly.

The blend door actuator motor is on the front side of the box and can be seen by fulling opening the glove box and looking to the left over the transmission tunnel. Pictures and diagnostic procedures are available at heatertreater.net.

The blend door on the Taurus is on a horizontal axis running from the front to back of the car. If you fully open the glove box, you can see the actuator motor in the far left hand side of the heater box. Access to the motor is trying, but not difficult. There is a metal cover held on with two screws and three additional screws that hold the motor in place. Additionally there is a miki-mauz lever system connected to the motor that controls the backside radiant heat door over the heater core. It is difficult to remove the lever system without breaking it.

If you pull the motor, you can examine the axle connector to the blend door and physically verify if it is broken. The Taurus has two major problem. 1) a block heater core and 2) broken blend door. The dealer solution to replacing the door is complicated and expensive.

It sounds like the control cable for the heater control valve may have slipped position, is now binding, or, that valve is partially blocked. Hopefully, the heater core needed replacing, and the heater control valve was'NT the problem all along. It is paramount that we find reputable and thorough mechanics. I'm not a mechanic, but I am a consumer who, like others, have been pinched before. Good luck on your thorough investigation !....BB

On a 99 Taurus, the blend door is controlled by an electric motor and this same motor module is used on multiple Ford products. The motor has the characteristic of over stressing the plastic blend doors when it goes through a periodic calibration routine. The net effect is a broken blend door and loss of control over temperature control. We have the Taurus on our development list at HeaterTreater and will have a simple cheap solution available this summer. As a stopgap, you can short circuit the coolant flow through the heater core and run in AC only mode for the summer.

The blend door actuator / motor is a rather common failure. Costs about $15, and the repair instructions can be found online (doesn't look too difficult with the ashtray & bracket removed)

See "Related Links" below

Nothing except normal plain old usage. They just fail. It is a motorized device built by human beings. It will and does go bad. There are plastic gears inside that wear out and electrical stuff that breaks down and dies.

If you mean that you can't mix the air (i.e. make the air warmer and cooler with the mixer knob) it may not be the valve. My 99 stopped mixing about 6 months ago with 94,000 miles. Then a couple of weeks ago the "tee" for the heater bypass hose sprang a leak. I had the hose assembly replaced, but the car started overheating when the engine speed was low, as in traffic. We got it home from New Orleans to Jacksonville, FL by adding water every two or three hundred miles. I then came to this site and decided to have the water pump replaced. When I got back to the garage, he showed me the pump. THERE WERE NO VANES ON THE PUMP!!!!! It looked like a little waffle on a stick. Now I know why it would overheat - not a lot of water was circulating without any vanes.

Try replacing the synchronizer assembly that is under the camshaft position sensor. I had to replace it in my 96 Taurus. I work in a repair shop and we have don't it in a 97 Taurus also.

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