Heater control valve

With fall here and winter approaching car heating problems can become just as important as air conditioning in the summer months.

No driver wants to freeze or burn while they’re driving their car down the road.


heater control valve

The heater control valve is one of the many components that are responsible for warming the interior compartment. This valve allows hot coolant to be piped directly from the engine to the heater core.

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The heater core then transfers the heat to the interior compartment by recirculating air from inside the car across the heater core fins.

This continued cycle of heating the air inside the vehicle is extremely efficient.

Heater control problems


climate control

Many things can cause low output from your car’s heater. Understanding how to heater control valve works can be important in diagnosis of this car problem. The heater valve sometimes called the water flow valve controls the direction and amount of coolant flow to the core.

In the closed position to heater control valve allows no hot coolant to enter the heater core. In the open position the part allows engine heated coolant to circulate through the firewall mounted core.

Consult your online auto service manual for specific locations on your vehicle.

Most heater control valves are operated in three basic ways. A manual cable, a thermostat type system, or even engine vacuum can control them.

Cable operated types are control directly from the control lever on the dash mounted climate control center.

Thermostatically controlled valves feature a liquid filled capillary tube located in the discharge air stream of the heater core. This will accurately determine the air temperature blowing at the driver.

A thermostat control valve will modulate the flow of hot water to maintain a constant temperature selected by the driver.

The most common type of heater control valve would be to vacuum operated type. These valves are normally located in the heater hose input line going to the core. They can also be mounted directly in the engine block itself.


Heater core

When a vacuum signal reaches the valve a diaphragm inside the valve is raised, either opening or closing the valve.

When the temperature selection on the dashboard is changed the valve is vented and then returns to its natural position.

Vacuum actuating heater control valves are either normally open or normally closed designs. Some vehicles do not use a heater control valve at all, but most do.

On modern vehicles it is hard to find a control valve that is not made out of plastic. This is great at reducing corrosion, but the lightweight of the valve can also make it unreliable Late in its life.

The most common causes for replacing a heater control valve would actually be an external leak from the valve body itself. If your vehicle has a lack of heat and this valve is not leaking.

Be sure to follow your diagnostic chart in your auto repair manual. Many other vehicles related problems could cause a no heat condition. The heater control valve is just one of these items.

You can visit my Diy auto repair website for more information on the theory and operation of automobile AC climate control.


  1. Thanks for the informative post – proper winterization, including maintaining and properly using your alternator and battery can prevent a lot of hassle.

  2. If it is no longer possible to turn the vehicle’s heat on or off, or if the valve leaks coolant, replacement of the heater valve may be necessary.

  3. Hi,I understand that these instructions are for those able and willing to repair their car themselves, but I just wanted to point out that we recently worked with a consumer that voided his warranty by working on his car. Basically, the consumer attempted to repair a heater that was later found to be a defective. The result was that he could not be compensated for this problem that was due to the manufacturer.

  4. Ok so let me first start off by saying I am a female and so bear with me if my questions sound “less than intelligent”. I have a 96 taurus with 111,000 miles on it and we have done everything under the sun to this car including within the last year, a frame (a southern part), new water pump, new brake lines, new coolant reservoir, new brakes, rotars and calipers.
    My question is: I have low heater output and I don’t want to have to pull the heater core out to replace! What could be causing this low temperature output? The fan is fine and the thermostat is fine!

  5. Kathy: Your question is a good one. The problem is that a 96 Taurus is not a good one (taurus that is)(Just my opinion)! The 96 was the first year of the rounded body style and had many inherent problems.
    The 2 big ones were cooling system problems and transmission issues. The cooling system issues can effect heater output. The cooling systems in these cars came with just regular old style green coolant that needs to be changed often. When not changed it can turn thick and brown quickly.
    This can lead to small clogs that can get stuck in the small heater core passages and reduce the heaters efficiency. Is this what is wrong with your car?? I don’t know!! This will need professional diagnosis. The heater core can be flow tested before replacement.

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