To find the refrigerant lines connected to the evaporator, you'll need to access the area behind the dashboard. This is a major undertaking and requires considerable mechanical skill, specialized tools (like refrigerant handling equipment), and knowledge of automotive AC systems. It's not a DIY job for most people.
If you're having AC problems, it's highly recommended you take your Vibe to a qualified automotive technician specializing in air conditioning repair. Attempting to work on the evaporator lines yourself risks damaging the system and causing further, more expensive problems.