560SL Klima issues

[My560SL]

Hello Everyone,
Long time reader that recently signed up as I have a problem with my 86 560SL AC and could find nothing via the search to help.
Everything seems to test OK, but the compressor will ONLY kick in if I bring 12 volts to it directly at which point the AC blows ice cold.
Right now it seems to be getting a dribble of power as the clutch ever so slightly engages, where by I get about 1 jerky/hesitant revolution every few seconds.
I'll list what i know thus far:
Charge is good (still R12)
AC Relay swapped with known good
Klima push button SWKG
Temp control relay SWKG
Cabin temp sensor SWKG
Evap temp sensor SWKG
Fuses/contacts have all been changed with copper and cleaned.

One thing that is strange is the aux fan is on all the time unless I pull the leads feeding it.

I'm waiting on my service manual from MBUSA with the hopes of printing off a wiring diagram but Any thoughts/avenues I might pursue in the mean time would be appreciated.

Many thanks to everyone!

Glen in NY

[Strife]

The fan is supposed to be on (low-speed) when the AC is engaged and there is sufficient "low-side" pressure in the A/C system. There is a switch for this.

[stevebfl]

If the engine is overheating, OR the controller thinks it is, the compressor will be shut off. I would investigate the fan problem!! I would suspect the temp switch on the motor. The normal way the fan comes on low with the AC is from the pressure switch on the drier. If the fan is on because of the engine switch the AC will shut off.

[My560SL]

Thanks Strife and Steve. The problem with my fan (it was on All the time) was the temp sensor; I unplugged them one by one and found the culprit.
The car is definitely not overheating, I've verified the temperature (she runs a rock solid 80-82 degrees) with a non-contact thermometer and the aforementioned symptoms happen all the time regardless of engine temp.

Glen in NY