Have you hooked up gauges to determine pressures? If overcharged, the pressure can actually be *too* high which will trigger the high-pressure switch and prevent the compressor from running. The pressure may just be lower in the morning and evening (due to cooler ambient temps) which may be allowing the compressor to run.

Just a thought...

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280