The compressor is ultimately cycled by the ETR (evaporator temp regulator) switch. It is behind and below the glovebox, accessible by removing the lower dash panel (relatively easy to expose -right in front). Unless the temp is getting cold it will never cycle. If the A/C is functioning properly the evaporator will freeze into a block of ice within a half hour in humid climates. If it can't make it below 50deg it might never cycle and it surely won't freeze up.
The same holds for the aux fan. It is activated by an engine temp switch of 212 degrees and a thermostatic switch mounted on the drier. The early thermostatic switches had to be pretty hot before they would set it off. If your A/C system is low or working poorly the thing will never creat the heat necessary to turn the fan on.
Bosch Master, ASE Master, L1
33 years MB technician