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Replacing the HVAC Vacuum Actuators

on the 1985 300D (W123)

by dmorrison


Just replaced all the AC vacuum elements on my son’s 85 300D. I did not take pictures since it would have been very difficult to get good pictures. But I will put to paper (actually keyboard ) my thoughts since I just finished the job.

There are 5 elements to replace in the dash. It is easier to remove the dash but more time consuming, sort of. The job took 2 days only because I needed parts in the middle of the job. With all the parts I would estimate my time at 8 hours (6 if you read this). Part of that was learning since I have not replaced the elements before while the evaporator box was inside the car.

So the parts needed are the 5 elements and about 15 of the lock washers and rubber washers that 2 of the elements use. 2-3 rivets to attach the center vent rod to the flap, you will probably drop some. Consider a new foam tube above the glove box in the dash, or a hard plastic replacement. Also consider a new rubber duct for the center vents if yours is deteriorated. A total of 6 lock washers are installed on of the elements. One element is extremely easy to put the washers and lock washers on. The other is a bear. It’s the center vent element. Make sure you buy and use the rubber washers. It makes it easy to remove the lock washer by inserting a flat screwdriver under the metal lock washer, into the rubber washer and twisting the rod off the element.

The other 3 elements are a “twist in and lock” units, so lock washers are not used.

To start the job I recommend the following:

Remove the glove box interior ( not the door, just be careful), the passenger under dash panel, the AC blower motor, the instrument cluster, the steering wheel ( even though it can be done with it installed ( couldn’t get my sons off), it’s easier if its out of the way ), the driver’s side under dash panel and the center vent rubber ducting inside the dash..


- I used a set of 16 inch long needle nose pliers to place the lock washers and rubber washers on the center vent element. As well as standard needle nose pliers.

- A small 10MM closed end wrench duct taped to a 12 inch long pry bar to press the lock washers on the center vent element.

- A MityVac and about 2 feet of vacuum rubber hose, enough to fit all the way into the center element and not be in your way while working in the glove box.

- And a U hooked scratch to release the Defroster element lock.

- Of course normal tools such as screwdrivers and etc.


Right to left as your sitting in the car.
I have labeled the elements

Now lets approach each element and discuss the difficulties and simplicity I found.

The Fresh Air/Recirculation Flap Element ( fresh air ).
You approach the fresh air element via the glove box and the blower motor opening. You may have to disconnect some electrical wires on the amplifiers just above the glove box so you can get your hands on the element. I used a 90 degree pliers to push on the locking tab and then rotated the element out of its holder. I also removed the 90 degree tube from the blower to the side panel to egress the element. The attachment rod is disconnected by moving it perpendicular to the rod shaft and installed in reverse, very easy.

The Main Air Flap Element.
This is the easiest. I broke the tabs off the element with needle nose pliers. SAVE THE LOCK WASHERS AND RUBBER WASHERS. Disconnect the rod by squeezing the 2 halves of the lock mechanism and the rod should come off the shaft.

The Center Vent Element.
This is the most difficult. First I suggest you remove the foam tube that connects the temperature element in the center of the dash to the blower motor housing. This is a good time to replace it with a new one or a plastic tube. This may be the reason why they used a foam tube. The foam section is in the way of removing the element, It has to be removed to get the old element out. To remove the element I used the long needle nose pliers to break off the element tabs. The top and bottom tabs through the glove box and the drivers side tab through the instrument cluster opening. Disconnect the rod to the flap by reaching through the glove box and pulling it off. Try to hold onto it or have a spare available for reassembly. If the center vent flap is in the closed position you can retrieve it. If it falls down into the evaporator box, kiss it good bye. I had 5 spare rivets (actually a plastic shaft with locking pegs on it). It is easier to remove the element from its mount if the rod is retracted. Apply vacuum to the element and it will allow you to twist it out of the mount due to the whole unit being shorter.

Now for the fun part, installing the center vent element. Apply the long hose to the element and retract the rod by applying vacuum.

Place the element into its mount via the glove box opening. Direct the element rod through the opening in the vent box so it may be connected to the center vent flap. You can view the rod positioning through the center vents. Flashlights and a utility lights are required. Once the element is in position you can release the vacuum to the element to allow the rod to fully extend. This allows you to attach the rod and flap actuator with a rivet with the center vent flap closed. This allows you to retrieve the rivet when it falls, not IF, but when. Attach the rod to the flap and then apply vacuum again. It helps pull the element towards it mount. AT THIS TIME I RECOMMEND A HELPER TO PREVENT COMPLETE AND UTTER FRUSTRATION. You must get the rubber washers and lock washer on the 3 small tabs in the center of the dash.

Using the 16 inch needle nose pliers I would hold a rubber washer with the pliers and slip it on the tabs. The top and bottom one via the glove box and the drivers side through the instrument panel opening. Place a rubber washer on the tab and then carefully force the lock washer on the tab “head” while the helper is holding the element against its mount bracket. You will notice that the new element has a head on the end of the 3 tabs. The head diameter is smaller than the rod shaft. It allows the lock washer to go on but much more force is required to seat the lock washer against the base. I taped a 10MM box wrench to a 12 inch long pry bar. The box wrench will press on the lock washer and seat it. Throughout the ordeal I had 4-5 lock washers pop off. They usually drop down on the top of the evaporator box and can be retrieved. 1-2 are gone and who knows where they are. So with patience, the helper holds the element, pushing towards the rear of the car and towards it’s bracket while you fumble with the pliers and washers to get all 3 rods lock in. Press them on tightly with the box wrench pry bar setup.

After you have done this disconnect your MityVac vacuum hose and install the AC vacuum hose. I found it best to reach one hand in each opening and use a finger on each hand to either push or pull the hose. A little silicon spray on the tube might help.

The Defroster Flap Element.
You’re over the difficult part so this will go faster. I did disconnect the electrical plug located just below the defroster element. This goes to the start neutral switch, so if your car will not stat after the job, you forgot to reconnect this harness. From under the drivers dash side you will disconnect the rod to flap via the same method used on the main air flap. Needle nose pliers to squeeze the locking tabs and pull the plastic rod out of the metal element rod. To unlock the element from its bracket I used a U hook shaped scratch all and pulled down on the locking tab while rotating the element. Replace it in the reverse order. The self locking elements go in easier then they come out.

The Legroom Flap Element.
This one is not bad but it requires a little work. From the passenger side I used the 16 inch needle nose pliers to disconnect the rod to plastic actuator. A small screwdriver was also helpful to complete the separation of the two. Once the rod was separated from the actuator I used a long screwdriver to force the locking tab out of the way. I actually broke the tab. From the driver’s side twist the element to remove it. Installation is easy.

Once all the elements have been replaced you have to reassemble the dash. The more difficult part of this is reinstalling the rubber ducting to the center vents. Apply the large opening to the evaporator box first. Put both hand into the dash, one via the glove box and the other via the instrument cluster. Force the rubber around the opening and make sure it seals. Reinstalling the vent openings works best if you first place the rubber on the most inner section if each vent and then work you way around to the outside last. Work the top and bottom at the same time. You can use a long screwdriver through the vents to position the rubber duct if needed. Once the rubber duct is installed then it’s a matter of reinstalling everything you took off to do the job. Or as the Service Manual says “Install in reverse order”.

I hope this helps I know that a Photo Technical Manual is best but getting pictures inside the dash was a pain so I quit while I was doing the job, they were not coming out.


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