can't run pg_dump in sh script using crontab

   Dear colleagues,

   Besides I am new to Postgres, I am new to linux too.
   I have a sh-script which run pg_dump by hand successfully. But
I have no results when I run this script using crontab. I haven't got
any error log.
      Please, help me.
      Here is my sh-script:

#!/bin/sh
PG_BIN=/ora/pgsql/bin
BACKUP_DEST=/ora/home/FOR_POSTGRES/backup/dump
$PG_BIN/pg_dump -f $BACKUP_DEST/`date +%d%m%Y`_cspb.dmp dbname

   PG_VERSION contains 7.0.
   File HISTORY contains "Release 7.0.3".
   I have a single version of Postgres, so pg_dump
is the same version.
I connect to linux as user "oracle". He has an access to
database "dbname" and can SELECT data using psql. As far as
I remember, I create this database as user "oracle".
I usually start postmaster as user "oracle".
And I edit crontab as "oracle".
As "oracle", I can run this shell script by hand and get a good
dump file.
   But I get nothing if I run it using cron.
   I think, may be oracle pg_dump can't find database
"dbname" when it runs by crontab ?

   Thanks,
   Slava