Some vehicles DO have a low-pressure switch on the suction side, usually vehicles with fixed orifice metering devices, that's how the compressor cycles. The Mercedes system uses the dual pressure switch to lock the system out on low charge and cut the compressor off on high head. Cycling is done based on cabin temp and/or evaporator temp switch (freeze 'stat).

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)