psql can't connect to old DB after installing new binaries

CentOS 6. I have a box with 9.2 installed and running, planning to upgrade
to 9.6. All packages are from the postgresql yum repos, not the CentOS base
repos.

However, after installing the 9.6 binaries, psql complains about the socket
file:

psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

My postgres 9.2 database has a socket file in /tmp/.s.PGSQL.5432. What's
interesting is that I get this error even when running the 9.2 psql as well:

$ /usr/pgsql-9.2/bin/psql
psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

$ /usr/pgsql-9.2/bin/psql --version
psql (PostgreSQL) 9.2.22

However I can connect if I specify "-h /tmp":

$ /usr/pgsql-9.2/bin/psql -h /tmp
psql (9.2.22)
Type "help" for help.

postgres=#

Also when if I remove the 9.6 binaries (yum remove postgresql96*), then
psql works as expected as well.

I can sort of understand the socket thing from the 9.6 psql binary, but not
the 9.2 binary. Either way it would break scripts for the existing DB,
maybe some other backwards compatibility issues. Is there something else to
change (other than unix_socket_directory, which would require a restart as
well) so that installing the 9.6 binaries wouldn't affect the 9.2
environment?

--
Don Seiler
www.seiler.us