It isn't necessary to jump the low pressure cut off switch in order to charge the system. As a matter of fact, it isn't even advisable.

There should be enough pressure generated by the initial installation (with the system turned off) of refrigerant to close the switch, assuming it is functioning properly. You don't want the compressor to run until there is enough refrigerant in the system to circulate the oil to the compressor.

It is difficult to make an absolute determination if a compressor is good without trying it in the system. You can get a good idea by, with the system off and the engine not running, turning the front clutch plate. The compressor should turn smoothly without any drag anywhere in its rotation. There would be a slight resistance due to the compression, but at hand turn speed, not much.

Hope this helps.

Ted

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Ted
1979 240D
165,000 miles