More:

Cabin Temp Sensor
Cleaned the vent. Since blower changes speed after changing temp wheel, I’ll assume this sensor is functioning.

Low Speed Fan
Jumped across pigtail connectors with screwdriver at receiver. Heard fan(s) come on.

Aux Water Pump & Duovalve
Pump & Valve are both hot to the touch. Hoses to heater core are not. Hot coolant flows only when heater/defogger are turned on.

Recirc
Goes on/off in EC mode. Goes On in A/C modes but not Off.

Pipes from Compressor and Receiver/Drier
Relative to the hot metal and plastic components surrounding them, the pipes going from the compressor, and leading to the Receiver, are cool to the touch. But not frosty.

Other
After driving for a while, especially w/blower on low speed, the air gets progressively cooler. Some might call it “cold,” but it is not nearly as icy as it was just 24 hours ago.

Recharge Needed?
I have a hard time believing I need a recharge since the system was charged in summer 2003 – when the evaporator, expansion valve, receiver and other components were all replaced, and fresh R134 w/dye was added. It seems unlikely the system would suddenly take a massive Freon dump when it was working perfectly the day before.

Then again, the weather has been very mild and I have used the A/C only about three times this summer, so perhaps something is dried out, stuck or whatever. What I suppose I’ll do next is examine the vacuum lines under the passenger dash. (And hopefully someone will tell me what that detached vacuum line is in the picture I posted above. )

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black