Mercedes: AC cuts out, mercedes benz 300sel, worldpac com

Question
1989 Mercedes 300 SEL  112,000 mi, Pittsburgh

My ac seems to cut off after 20-40 minutes of operation
Some observetions:

I think it tends to do it more often when outside temperature is over say 88 deg.

Sometimes it seems as though after cold air cuts off, if I turn engine off and restart / ac resumes.

Answer
Answer:
My best guess would be AUX cooling fan not turning on.
* Failed A/C temp switch
* Failed AUX fan

Note:  @ receiver drier
Located on receiver drier for auxiliary cooling fan. Identified by 2 spade terminals on short pigtail with red base.     
R1055-29376 A/C Temp. Switch   ACM    IN STOCK
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Vehicle: 1989 Mercedes Benz 300SEL
Part: Auxiliary Fan Assembly
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