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Heater Control Valve

This component is part of Heating System.


The Heater Control Valve controls the flow of radiator fluid through the Heater Core inside the W113. It moderates the flow of fluid, controlling the amount of fluid (& heat), as well as, it controls the on & off of the heat inside your car.

Heater Control Valve O-Ring Replacement

If the heat inside the car doesn’t want to shut off, it could be that the o-ring on the heater valve needs to be replaced. The following procedure will help you to replace this rubber o-ring…

1. Remove the heater valve access cover. This is the large rubber/plastic cover on the firewall, above the return heater hose.

2. Stuff a rag around the valve and ensure that the rag is positioned all the way around the valve. This will help to catch anything that may get away from you. If you drop any tools or parts into this access hole, you will need to remove the fan box and possibly the entire heater core to retrieve your lost items.

3. Take some pictures and make note of the position of the valves arm as well as the position of the heat sliders inside the car. Either slide the heat to the fully on or fully off position. Again make note and take pictures of the valves arm position under the access cover. You want to reinstall in this same position.

4. Carefully pry off the rod connected to the top of the valve arm and set off to the side.

5. Carefully unscrew the screw that holds the valve arm and remove the arm.

6. Use a long metal screw (screw threads = 4 x 0.7 mm) and carefully screw this into the hole of the valve (refer to picture in step 13 below). This will help to pull the valve from the core. Before starting to pull up on the screw (valve), tie a string on the end of the screw. Secure the opposite end of the string to a stationary point (ie wiper arm). This is to help ensure that the valve doesn’t fall into the core. If the valve falls into the core, the core will need to be removed from the car.

7. Carefully tap down on the screw to lower the valve so that the metal stop plate can be removed from the side slit in the core.

8. Make note of the exact position of the stop plate. It will need to be reinstalled in this same position.

9. Remove the screw and slide the metal stop plate out. Screw the screw back into the valve.

10. Carefully pull up on the screw/valve to remove it from the core. You may need to use a pair of pliers to assist with removal.

11. Once the valve is out, take to the bench and remove the old rubber o-ring and clean up all parts.

12. Install new rubber o-ring (PN# 000 835 41 98)(17mm OD x 12mm ID x 2.5mm Thk). Also lube the valve ad o-ring with some plumbers grease. This helps to slide the valve back into the heater core.

13. Reinstall the valve (with the long screw secured with the string).

14. Ensure that the valve is installed in the same position as when you removed it.

If you do not remember or are not sure always install the valve in the open position!

Insert a wire through the front pipe as explained below to assure that valve is open.

With the new rubber o-ring, the fit should be nice and tight as you slide it into position. Carefully remove the long screw. Again, the valve should hold in place with the friction of the new o-ring.

15. Carefully install the metal stop plate & on/off arm in same position as when you removed it.

16. Carefully install the on/off rod onto the arm.

If the valve is in the open position the on/off lever will be pointing to the cabin!

17. Remove the rag and reinstall the rubber/plastic cover on the firewall.

18. Congratulations! You are finished!

Another view of the open (heat on) and closed (heat off) position of the valve lever. The position can be checked by feeding a wire through the opening and monitoring the length of the inserted wire (green arrow).

And Another Operational View

Note how the left, lower red lever when moved to the left pushes the wire forward (direction of engine) that pivots the flap from a vertical to a horizontal position and at the same time the flap pulls the linkage backward to open the valve allowing hot water to flow through the Heater Core.

When the lever is moved to the right it pulls the flap vertical which in turn pushes the linkage forward closing the circulation through valve. In the vertical position the flap closes the passage way for cool air through the heat exchanger as shown here:

Fresh air will flow in front of the exchanger and down into the distributor box but since hot water is not circulating through the Heater Core it will not be warmed, provided of course the valve closes completely.

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