95 e300d - a/c blows cold from center vents, outside vents blow hot. Classic duovalve failure according to lots of searches here. Bought the new one from dealer. They call it a water valve. Basically it has an on/off valve and a small pump.

Removed battery
Removed expansion tank cap
started removing hoses (5 in all)
Lots of g-05 leaked out. I used rags and towels. I didn't want to drain the entire system. This was probably a mistake.
Installed new unit and connected hoses.
Added more 50/50 g-05 to expansion tank.
Went for a drive.
Heard a little whirring noise for a block or so, then it quieted down.
After reaching operating temp, blows cold in center and not hot from sides.
Rechecked hose connections and drank a victory brew.
Returned to scene of the crime to find a puddle of g-05 on the garage floor.
Replaced weak MB hose clamp with classic wide Made in USA hose clamp.
Topped up and took for extended ride. No leaks and heat/cold seem to work fine.
2.5 hours from start to finish including second leak fix.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900