Can't create Collection using ClearCollect Function

[carem]

I encountered a challenge when following the guidelines of this article.
In the Step: Writing the related schools into a collection

Faculty Field -> OnChange: 

ClearCollect( collSchools, { Schools: Filter( Schools, Faculty.Value = DataCardValue2.Selected.Value ) } )

Property Explanation

collSchools	This is our collection where all related schools for the selected faculty are written in to
Schools	This is the name of the column where the data is written in to
Filter	This is the function that filters values from a data set. The format of this function is as follows: Filter(source,logical_test)
Schools	This is the data set that we use in our filter. In this case, it is the Schools list we added as data source
Faculty.Value	This is the value we are looking for in our data set. In this case, it is the Faculty lookup field in our Schools list
DataCardValue2.Selected.Value	This is the selected faculty from our PowerApp

I follow this fomulas but the result is an empty collSchools Collection.

Here is my Form Setting

And the OnChange of Faculty Dropdown:

And the collSchools Collection: Empty School Column

Can anyone help me resolve this problem?

[RezaDorrani]

@carem 

Ok so it means something is incorrect in your data

CountRows(Filter( Schools, Faculty.Value ="hardcoded value" ))

When you go to SP list Schools - does it have any data? I am assuming Yes

Does it have values in Faculty column - see the values there

then try and hardcode that value exactly in the hardcoded value in formula above and test

[carem]

@RezaDorrani 

I have discovered a serious problem with Preview Mode. I think it is the cause of this problem.

My Preview Function is not working. It's mean when I press F5 you can see my form like this:

Edit ModePreview Mode

It may be that it cannot recognize the value of drpd_Faculty.Selected.Value. And return an empty Collection.
Follow Pstork1's advice, I create a button with OnSelect Property:

ClearCollect( collSchools, { Schools: Filter( Schools, Faculty.Value = "Faculty of Health" ) } )

And it's work.

But when I go back for  

ClearCollect( collSchools, { Schools: Filter( Schools, Faculty.Value = drpd_Faculty.Selected.Value ) } )

It does not work anymore.