Vouloir means something different when used in passé composé and imperfect. When used in the passé composé, it expresses an unfulfilled wish in the past. In the imperfect it simply states the fact that you wished for something, without implying that you didn't get it.

Je voulais te voir, alors je t'ai rendu visite. -- I wanted to see you, so I visited you.
J'ai voulu te voir, mais je n'ai pas eu de temps. -- I wanted to see you but didn't have time.