How to connect to a database psql doesn't see

I have a database (timetrex), which is accessed via a web page, located
on an Ubuntu 12.04 Sever. I can trace all the files and it's producing a
regular .sql backup file each day (or maybe each time it is accessed via
the web page).
When I attempt to access it using the psql -l command as user Postgres
it does not show.

Over time timetrex seems to have created a Postgres 8.3 database and a
postgres 9.1 database in the /var data path and neither shows up.

Before I update timetrex to the latest version I would like to know that
in an extreme case I can run the .sql backups to restore my data but to
do that I need to be able to see the database.

Is there a way to run the postgres client pointing to the path for the
database files I have identified so it does see my timetrex database?

Thanks

Mick