My R4 compressor developed a massive leak around the outer seals. So I needed to replace with a new one. The compressor warranty requires that a new expansion valve also be installed. Whoever wrote the factory manual page on replacing the expansion valve in a W126 300SD should be !@#$% slapped.

He/she wrote:

1. Drain air conditioning system.

2. Remove cover at left under instrument panel.

3. Open housing by half.

4. Loosen all hose and pipe lines on injection valves with box end wrench first and then screw off.

The manual fails to address the large (6" diameter) tube that routes heater air on the driver's side that must be removed. This requires removal of the instrument cluster to get to the bolt that secures the tube on the right side. The manual fails to address the metal brace that is attached to the transmission hump with three bolts and is bolted up under the dash in two places. Not to mention the numerous bundles of wires that are cable tied to the brace. You cannot remove the brace to get it completely out of the way because of the routing of one of the wire bundles, so you are fighting the brace during the rest of the process as its natural resting place puts it right in the way. Also you need to remove several pieces of plastic ductwork just to see the expansion valve.

A 17mm flare wrench will work on one lower fitting on the expansion valve. I was able to use a 21mm crow-foot with a 6" extension on the other lower fitting. You cannot use a wrench of any type on the upper fittings. You can get a wrench on one of the fittings, but there is no room to turn the wrench. A 19mm crowfoot did work on one upper fitting. However, when you get that first fitting screwed out, it is still in the way so that even the 21mm crow-foot will not have room to slip onto the other fitting. I had to take a chop saw and grinder to my crow-foot and narrow down the sides to be able to slip it on the fitting. Then it was "turn the socket wrench handle about 20 degrees, then remove the crow-foot and reposition for another turn."

Finally the thing was out. Pic 1 shows the debris in the system. Note that the compressor had not failed--this was just a dirty system.

Took close to 2 hours just to get the valve out.

I drilled out the old valve so I could reinstall it to aid in flushing the evaporator. Worked great. Pic 2 shows the new undrilled valve and Pic 3 shows the old drilled valve.

Reinstalling with new o-rings was just as much fun as getting it out. I have left the brace, tubing, etc. loose until I can finish the project so I can check for leaks. Unfortunately, after installing the compressor and the drier, I discovered another leak, this one in the condenser, so I had to order another condenser. OUCH.

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1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead