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It might kick on when you hook up the can, but more than likely you'll have to put more than one can in to make the switch bypass.

Someone jump in here if im wrong, but I think the full capacity of that compressor is like 3 cans. Half of one can replaced by compressor oil. In the front of the radiator on the drivers side behind the grill, there is the dryer with a clear glass eye on the top, continue to add freon untill the bubbles in the sight glass go away. That is an old school way of monitering the level of charge in the system. Be carefull here, dont over charge the system or you could damage it or yourself!

Did you have problems with it before it quit working? Or was it just all at once? Sounds like you got a leak to me if there were enough refrigerant (and oil) gone to enable the pressure switch to activate.