If my ac is not charged will the compressor not come on?

The clutch will still kick on, if its working properly

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99 Jetta Mk3
07 Jetta Mk5
89 300E W124
10 E 350 W212
08 C300 W204
Benz's aren't mine

i was told , if there is not enuf Freon the system will not let the a/c pump clutch to work, some sort of protection to prevent the pump to run dry. Some sort of pressure sensor hooked to the system. One can always run 12 v to the pump terminal, and see if it cools down.
correct me if wrong.

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