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Removal and Replacement of Expansion Valve

1989 560 SEL (W126)

Considered a dreaded project by some, removing and replacing the expansion valve (located a few inches above the gas pedal) is not as bad as it seems. It took me about 5 hours, much of the time spent simply trying to figure out how to remove three components (steps 9, 10 and 11). Had I had this documentation here, I would probably have done it in much less time. Had I not had the kind help and support of my dear friend Chuck Taylor of Falls Church, Virginia, I would have taken much longer. 

I recommend reading over the entire procedure before tackling the job.

The following instructions assume an empty system (no refrigerant in the system) and do not include the refilling of the system.

The following tools are needed:

The following parts and accessories are needed:

 

Notes before getting started:

The two important aspects of getting this job done involves the loosening and partial removal of a support bar, with one of the bolts holding it in place being behind the instrument cluster, and getting the new expansion valve in place correctly.

One technician at a Benz service center told me that the vital challenge in doing this job right involves the correct setting of the threads when installing the new valve. He mentioned that too many of these Benzes have the job done cheaply at a corner shop, only to have the car come into his hands because some mechanic cross-threaded the hose and pipe connections. He then echoed what another technician told me: when installing the new valve, tighten the four connections by hand first. Keep everything loose (halfway down the threads at the most) until you have all four connections in correctly, then tighten all four all the way down the threads by hand, and then apply the wrench.

 

About the crowfoot wrenches:

I have been given different specs on different wrenches needed, going all the way to 24mm. On this model year, I now know for certain that you only need two crowfoot wrenches, 19mm and 22mm. However, the shape and thickness of the wrenches matter. I bought an entire impact set for about $36 on the web, only to find out that they were too fat to fit, and had a nasty shape problem that kept them from sliding onto the connector heads.

I found that the Sears Craftsman 19mm worked nicely. I did not get a chance to try a Sears Craftsman 22mm (dont even know if they make one), but found Snap-Ons 22mm to work perfectly. Both of these had simple U shaped  (open end box wrench) openings.

 

About the A/C oil:

I am assuming you know about A/C systems, their oils, etc. Never ever mix and match r12 oils with 134a oils, unless you know exactly what you are doing. Use the same oil type that is in your system. For this part of the job, you will be oiling the o-rings only. You will need more oil to add to the Receiver-Drier before refilling the system (not covered here).

 

Duct tape:

I found a drain hose in need of repair (Figure 5 D). I did not have the part handy, so I followed Tom Ridges advice of solving the problem temporarily with duct tape. Since I would not be surprised if this part had deteriorated on other models of the same vintage, I would apply the old motto be prepared. I have ordered a replacement part.

 

Benz Instrument Cluster pullers:

You can make your own with thin steel rods. I have experimented with several materials, including coat hangars. Short of getting the actual tools, by far the best material I found are the control rods for model airplanes, found in hobby stores. They are thin yet strong.

 

Below is a picture of what the Benz cluster pullers actually look like:

 

 

Figure 1

 

Total length without handles is 6.5. Hook length is inch measured from the outside of the rod, slightly bent upwards at an angle. The dimensions of the hook are important. The depth marker is at 3 13/16 from the top (or roughly 2 from the bottom), right by the tip of the pen. You can create you own mark using magic marker on your homemade tool.

 

The job:

  1. If you have a telescopic steering column, move it all the way out.
  2. Disconnect the battery (keeps all the lights off, and is a good practice anyhow).
  3. Remove all drivers side floor matting (admitted, I did this later, but doing it now is a great idea. Read on and youll know why! Also, some of the pictures were taken out of the sequence I am describing here.)
  4. Remove the lower dash: The lower dash comes in two parts the soft vinyl part closer to the driver and the hard plastic part over the feet. Removal is easy:
    1. Pull out the gray plastic Philips slotted retainers (Figure 2 A)

    

     

Figure 2

    1. Pull out the Phillips-headed metal screw (Figure 2 B)
    2. Remove the plastic strip moldings over the coin basins on both sides of the steering wheel by gently prying them away with a small screwdriver. They pop right off.
    3. Remove the screws underneath the moldings you just removed (Figure 3 A). Do the same above the ignition key.

 

Figure 3

    1. The upper part of the lower dash may fight you a bit not to worry, its stapled to the hard plastic bottom part, though not tightly. I found the best thing is simply to remove the staples (example in Figure 2 C) for good the grey plastic retainers hold both the upper and the lower portion in place.
    2. The upper part of the lower dash should come right off.
    3. The lower portion is held in place only by a metal T sliding along a long slot. I had to bend the T a bit to aid in removal.
    4. You will now be able to see the expansion valve, with the insulated cover, as shown in Figure 4. Chances are its been leaking refrigerant, oil, and dye. The lower plastic portion of the lower dash you have removed probably has some drippings, and since you thankfully have removed the floor mats as described in (1) above, the drippings are now going on the floorboards rather than the carpet! Note that by now you have probably worked for only about 15 minutes.

 

                       

Figure 4

  1. Take a breath, look at the project. You will notice that there is a big duct (Figure 4 A) in the way it needs to go (more on that later). You will notice that there is a plastic duct (Figure 4 C) behind the big round metal duct it needs to go. You will also notice a black steel bar (Fig 4. B) conveniently placed right by the expansion valve youll have to loosen it and move it out of the way (you cant remove it completely because there are too many cables wrapped around it at another location more on that later). The expansion valve cover is probably soaked with oil  - a perfectionist would replace it (I did not).
  2. Remove the center console side panel. There is a Phillips-headed screw (Figure 2 D) that needs to be pulled. The panel is very flexible and can be carefully removed after moving the drivers seat back all the way. CAREFUL: There are several plastic tabs that go into the molding of the center console dont break anything!
  3. Remove ductwork A in Figure 5 by removing screw B and sliding duct C out of the way.

 

Figure 5

  1. Remove the instrument cluster:
    1. Its a good idea to use Scotch tape to cover the wooden portion of the dashboard. There are sharp corners on some of the connections on the back of the cluster that can scratch the woodwork.
    2. Slide the MB tools into the cluster on points A and B up to the markings on the tools.
    3. Turn the tools to grip. (Figure 6)

 

                       

Figure 6

    1. Pull out the cluster (Figure 7). This will take some force and wiggling. DANGER: Do not damage the instrument cluster housing. Its soft, and Ive had a home-made tool bury into it (fortunately in a spot that cant be seen with the cluster in place). You dont want to add vinyl repair to the project

 

 

Figure 7

    1. Note the positions of all the connections carefully they are quite logical, but the better you understand them, the easier it will be to put them back in.
    2. Some connections may need the help of a small flathead screwdriver to create the first break away from the pins. Remove all connections and remove cluster.
  1. From below, remove plastic duct (Figure 4 C). It simply pulls out and is not retained by anything hard. Some twists and turns and it will be right in your hand.
  2. Remove round duct. It is held in place by two nuts (Figure 8 A) and by a bolt on a bracket off the steering column accessed from below  (hard to see at first, but approximate location behind and above duct in Figure 9 A, and easy to get to once spotted)..

 

           

Figure 8

 

Figure 9

            Also remove the grey Phillips headed fastener on the right of the duct holding in place the plastic duct manifold (Figure 10)..

 

           

Figure 10

            After closely examining the steering column mount of this duct you will find that it comes off the bracket by pushing it towards the drivers side, thereby clearing the tab. You may need a screwdriver to pry the mount away from the column to clear the tab..

 

  1. Ah now you have a better view! Time to loosen the black crash bar:
    1. Remove the bolt behind the instrument cluster (Figure 11 A)

Figure 11

    1. Remove the bolt under the steering column (Figure 12 A)

                       

Figure 12             

    1. Remove the fasteners by the center console. Figure 13 shows some of the locations (Figure 13 A) with the nuts already removed.
    2. Note position and remove the twist ties (Figure 13 B) and the other items (Figure 13 C are some that just pull right out) that may be impeding the movement of the bar.

                 

Figure 13

  1. The foam covering the valve is split and can be easily lifted. (If you tear it off (as I did) you can tie it back on later with a cable tie). Look at figure 14 (valve removed) and check the size of the wrenches needed.

                 

Figure 14


  1.  You can now remove the fittings. Dont be too violent they come off easily (no high torques), and you dont want to damage the top pipes that go straight into the evaporator! After removing the last connection, the unit should fall right into your hand. Tips on removing (as shown in Figure 14 above):
    1. Top left 22mm Crowfoot
    2. Top right 19mm Crowfoot
    3. Bottom left 22mm Crowfoot
    4. Bottom right regular 17mm open ended box wrench
  2. Remove the old black o-rings and clean the fittings. Oil the new o-rings with the A/C oil you bought and place them over the fittings.
  3. Installation:
    1. NOTE: If you are NOT replacing the receiver/drier, you need to add the right amount of oil into one of the hoses before connecting!
    2. Remember the two top connections (22mm and 19mm) are rigid, and the bottom ones loose hoses. Screw in the top connections about half way (no more and no less you want the part to wiggle, yet you want to make sure you are not cross threading) into the new valve.
    3. Connect the bottom hoses. This is the tricky part, and you may have to loosen the upper connections further again to get the valve into the correct angle.
    4. Tighten all connections all the way down by hand. This guarantees you are not cross threading before applying the wrenches, and will actually save you time in the awkward spots. Apply the wrenches. Remember that these were not too tight connections when you loosened them.
    5. Reinstall insulation. In my case, I used a long cable tie to go around the back insulation and back to the front to hold the front pad in place.
  4. To close up the job, reverse steps 1 11.
  5.  Replace receiver/dryer, with correct amount of oil.
  6. Vacuum and fill the system.

 

Note: Oil quantities on this model called for a total of 40 ml, with refilling system requiring 10 ml and replacing the receiver/dehydrator 30 ml

 

 

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