The Evap temp switch should cut the compressor off when the evaporator temperature gets close to freezing. If it has failed or is way out of calibration, the evaporator can freeze up on a humid day. When that happens, the system will blow warm or if it's frozen bad enough, won't blow at all.

What refrigerant are you running? That isn't specified anywhere in this thread. If you're running 134a, your suction pressure is low. Make sure when you're measuring pressures that you have all windows open and the system defaulted to max fan speed. Low airflow from the blower being on low or the evaporator being dirty/frozen will cause low suction pressures. If you know the coil isn't frozen and you have good airflow across the coil, you have a restriction in the refrigerant system somewhere.

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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!)