Method or technic to know how many times a value is repeated in the array?

I'm not sure if I'm understanding the problem properly, but I'm thinking you might be able to solve this by creating an array of counter variables that mirrors the array. (Or maybe this could be better implemented with some sort of object that has a value property and a counter property, and then you have an array of that object. I dunno.)

So you could try something like this:

for var i = 0; i < dConv.count; i++ {
    if dConv[i] == Intervalo1[0] {
        counterArray[0]++
    }
}

Also FYI I cleaned up a few things in your code that I just think make it easier to read. I did i < dConv.count instead of i <= dConv.count - 1. I did i++ instead of i = i + 1. Also, to test if two values are equal, you can just use == instead of checking both <= and >=. Same results but I think it's cleaner code).

I'm also wondering if it would help you to have a loop within a loop so that you can test all the values of one array against all the values of another. Something like this:

for var i = 0; i < Intervalo1.count; i++ {
    for var j = 0; j < dConv.count; j++ {
        if Intervalo1[i] == dConv[j] {
            counterArray[i]++
        }
    }
}

EDIT: Sorry for some reason the explanation I gave in the middle paragraph of the other minor edits I made to your code is getting messed up, whether I try and use backticks or just regular text the code and surrounding text is disappearing. Sorry.