Refresh yourselves on opening the bidding 1 of a minor by reading this post:
Opening the Bidding 
When you open the bidding 1 of a minor you only promise a THREE card suit.
That makes sense.  
With three ♣ AND three 
♦ ALWAYS open the bidding 1♣.  No matter how bad your ♣ suit is and/or how good your 
♦ suit is.  So with the following hands open the bidding 1♣:
  
    | Hand A | 
    Hand B |   
    Hand C | 
    Hand D |   
  
  
    | ♠Q62♥K873♦AKQ♣854 | 
    ♠A632♥K83♦AQ4♣964 | 
    ♠AK83♥KJ3♦AK4♣542 | 
    ♠AQ3♥K832♦KQ8♣432 | 
  
This makes less sense.  Why would I want to do that?  Wouldn't I like to tell Partner about my nicer minor?
No.
The reason we do this is this gives us a quick way of letting Partner know we have FOUR 
♦ in our hand when we open 1
♦.
I know what you are thinking.  So this means when I open 1
♦ I show a FOUR card suit?
No, you just show a THREE card suit.  BUT if you always open 1♣ with three ♣ and three 
♦ then the ONLY time you open 1
♦ is when you have two four card majors.  Therefore if Partner responds 1 of a major to your opening 1
♦ bid and you DON'T support them you MUST have FOUR 
♦.  
Let's see this in action: 
Hand A:
♠AQ62
♥94
♦Q983
♣AJ6
What will you open the bidding? 
You have 13 HCP.  You cannot open 1 of a major because you do not have a FIVE card suit.  You open your LONGEST minor.  Which is 
♦. 
So you open the bidding 1
♦. 
Now Partner says 1
♥.  What is your response? 
Partner is showing at least 6 HCP and at least four 
♥.  You cannot support Partner.  But you do have another four card major you can tell Partner about.  Your response is 1♠. 
This tells Partner you have four ♠ AND also tells Partner you have FOUR 
♦.  After all you do NOT have four 
♥.  You would have supported Partner if you did.  Therefore you have four 
♦. 
Hmmmm.  There MUST be a hand that does not have four 
♥ and also does not have four 
♦...
There isn't.  Take away one of the 
♦.  Where do you put it?  You still have to have thirteen cards!  Can you put it with your ♠ suit?
No.  Then you would have this hand:
♠AQ642
♥94
♦Q98
♣AJ6
and you would have opened the bidding 1♠ because you have FIVE of them.
What about this hand?
♠AQ62
♥942
♦Q98
♣AJ6
No.  You have three 
♦ and three ♣.  You would have opened the bidding 1♣.  
What about this hand?
♠AQ62
♥94
♦Q98
♣AJ63
No.  You opened your LONGEST minor, remember?  Here your ♣ are LONGER than your 
♦ so you would have opened 1♣.
The ONLY hand you will open 1
♦ with a THREE card suit is when you have a hand similar to this:
♠AQ62
♥K964
♦Q98
♣K3
This hand you must open the bidding 1
♦.  But now when Partner responds 1
♥ you can support your Partner's 
♥ suit and would rebid 2
♥ to let Partner know you have a fit. 
Does this work the same way with ♣?  If I don't support my Partner's major after I open 1♣ do I promise four ♣?
No.  The only reason it works with 
♦ is because we choose to open 1♣ with three cards in both minors instead of 1
♦.