Help identifying engine parts

[Richard 1992 SC400]

I recently purchased a 1992 SC400.  Can anyone help me identify these two parts?  The first part sticks out of the front of the engine between the A/C compressor clutch and the main engine pulley.  It has a single wire coming out of it that leads to a connector.  Something in the part is leaking on the A/C compressor clutch, and I would like to replace it, but I do not know what it is.  The second item is a canister that sits near the brake fluid reservoir and it says Nitrogen Gas Under High Pressure.  What is it, and what does it do?  Attached are a few pictures.  Thanks for your help.