What person(s) of the Trinity were the people of the Old Testament interacting with? When a someone or groups of people were interacting with God, as recorded in the Old Testament, in general were they simply interacting with person of 'God the Father' within the Trinity? Or were they interacting with the 3 in one at the same time? Or where they sometimes speaking with the 3 in one, and sometimes God the father?

Perhaps I have a fundamental misunderstanding what the Trinity is, but the reason I am asking I because I am wondering if the second and third person of the Trinity ever interacted with humanity prior to the incarnation of Christ?
John 6:46
  οὐχ ὅτι τὸν πατέρα τις ἑώρακέν εἰ μὴ ὁ ὢν παρὰ τοῦ θεοῦ οὗτος ἑώρακεν τὸν πατέρα 
  
  Not that anyone has seen the Father except he who is from God; this [one] has seen the Father.


Nobody has ever seen the Father. 

If they saw God in the Tanakh (and, they did), then it was not the Father.

Conundrum?

No. I can quote many Early Church Fathers who insist that they saw pre-incarnate Christ. But, hey, let's dig a little deeper, shall we?


  John 12:41
  Isaiah said these things when he saw his glory and spoke about him.
  
  Isaiah 6:1
  In the year that king Uzziah died, I also saw Adonai sitting upon a throne, high and lifted up, and his train filled the temple. 


So, they saw the pre-incarnate Son of God. If you read the targumim (Aramaic translation/ interpretation of the Hebrew Tanakh), you will see that in many places where it says that YHVH is interacting with His creation, the targumim say that it is the Meimra d'YHVH (Word of YHVH) interacting with the creation.

Quite phenomenal if you ask me. =)