A. Cuando regrese a los Estados Unidos, tengo que conseguir un trabajo. |
When I return to the United States, I have to get a job. |
| B. Tenía que conseguir trabajo cuando regresé a los Estados Unidos. | I had to get a job when I returned to the United States. |
Example A uses the subjunctive because returning to the states (regrese) is still in the future.
Example B uses the preterite because the action is completed. Just because
the action is in the past does not mean that it must use the preterite. If the
sentence had refered to an action that was not completed in the past, i.e.
Me dijo que tenía que consiguir trabajo cuando regresara a los Estados
Unidos.
it could take the imperfect subjunctive.