My daughter’s 04 Trailblazer AC is very weak. I have added uv dye in the system, found major leak behind ac compressor. I’m not sure what it is but looks like some kind of port? Do I need to replace compressor or possibly rebuild that portion only?

 

pretty sure that is the high pressure relief valve. put manifold gauges on the system and check the high side pressure. if its around 200 ish the system is not running over pressure. (I think the blow off pressure is 450ish??550??)
not sure if you can replace the valve itself or if replacement parts are available. Your call.
myself, I don't want to go back in a second time if it leaks...replace compressor.

 

Ok. Understood. Thank you for advise!