When did Jesus send the Holy Spirit? I've always assumed that the Holy Spirit did not make his presence known amongst men until Pentecost.  Famously, in Acts 2, the Spirit descends upon the first believers, gives them power of speech, and adds tremendously to their power.

Jesus clearly foretells the coming of the Holy Spirit in Acts 1 - just before he ascends into heaven - saying:


  But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.” After he said this, he was taken up before their very eyes, and a cloud hid him from their sight.


That Jesus must go away before the Holy Spirit comes is attested to in John 16:7


  But very truly I tell you, it is for your good that I am going away. Unless I go away, the Advocate will not come to you; but if I go, I will send him to you.


All of this fit my narrative neatly, thinking, okay - Jesus takes center stage until He returns to the Father, at which point the Holy Spirit comes onto the scene with tongues of fire and such.  Sure, he may have "descended on Jesus like a dove" at Jesus' baptism, but he was pretty much quiet in the affairs of men. And indeed, as an eternal pre-existent being much like Jesus, I assume he was around, just not so much involved in the day to day affairs of men.

But then, I listened closely to the lectionary this week. I heard something in John 20:22 that I was not expecting.  After Jesus appeared to his disciples, after the resurrection, he said:


  And with that he breathed on them and said, “Receive the Holy Spirit." 


This seemingly contrasts with a non-involved Holy Spirit.  I thought that Pentecost was the "firstfruits of the spirit," the first time the Holy Spirit deigned to dwell amongst men.  Am I off my rocker, or am I missing something?  

In others - was 


a. Pentecost supposed to be the first appearance of the Holy Spirit, or 
b. am I just making up the idea that Pentecost was supposed to be the first outpouring of the Spirit?  


If (a), how is John 20:22 reconciled?  If (b) how could the Holy Spirit come in light of John 16:7?

In other words, when did Jesus send the Spirit, and how does it fit with the external witness?
The meaning of John 20:22 is clear in its context:

19 On the evening of that first day of the week, when the disciples were together, with the doors locked for fear of the Jewish leaders, Jesus came and stood among them and said, “Peace be with you!” 20 After he said this, he showed them his hands and side. The disciples were overjoyed when they saw the Lord.
21 Again Jesus said, “Peace be with you! As the Father has sent me, I am sending you.” 22 And with that he breathed on them and said, “Receive the Holy Spirit. 23 If you forgive anyone’s sins, their sins are forgiven; if you do not forgive them, they are not forgiven.” John 20:19-23 (Bold added)

The disciples were alone with each other. Not only that they were hiding from the public and those that would kill them. Jesus appears before them then address them, specifically. Jesus sent the holy spirit on them only.
Again in John 16:7 Jesus is addressing the disciples only. He goes on further to say that the disciples will not be able to be effective without the Spirit because the disciples alone do not know the Truth of which Jesus was speaking.

13 But when he, the Spirit of truth, comes, he will guide you into all the truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. John 16:13

The disciples were incapable of building up the church without the Holy Spirit. Peter was incapable of delivering likely the most convincing testimony ever in Acts two without the Holy Spirit. They were &quot;pierced to the heart.&quot; The exact dwelling of the Holy Spirit. It was at that moment that the Holy Spirit was &quot;outpoured&quot; on the people. It was freely given from that moment forward. The times before this moment it was necessary to be given to some so that hearts may be pierced and the whole world might believe.

So in specific answer to your questions:
A: No, Pentecost was not the first &quot;appearance&quot; of the Holy Spirit. That is clearly shown in the Scripture. It was, however, the first outpouring. Pentecost marks the day that the Holy Spirit was freely given to any who might believe.
B: It seems so. There is much evidence that the Holy Spirit was quite active and always has been, but only for certain persons. As Luke Ritchie has already said, this study shows that well, from the Spirit giving life in Genesis to It guiding the prophets. One thing to note is that The Spirit only does what is commanded by the Father and subsequently Jesus, too.

14 [The Holy Spirit] will glorify me because it is from me that he will receive what he will make known to you. 15 All that belongs to the Father is mine. That is why I said the Spirit will receive from me what he will make known to you. John 16:14-15

With this, one might interpret that God and Jesus almost always act through the Holy Spirit. A notable exception would be Moses.