When we have two verbs which are connected with να, the first verb is in Present or in Past or in Future Tense, but the second verb is always in Subjunctive Form (Future with να instead of θα). The second verb never changes.
Θέλω να φάω = I want to eat.
Ήθελα να φάω. = I wanted to eat.
Θα θελήσω να φάω. = I will want to eat.