-replace linebreaks ("`n,"") or ("`r,"") is not working with my Content

Hello everybody,

i'am trying to replace linebreaks from my content which i'm getting from a text file.
But it never replace the linebreaks with nothing. (i can replace spaces..woohooo)

This is what im trying (only e.g.)

$input_path ="C:\input.txt"
$input = Get-Content $input_path
$input_clear = $input -replace " ","" | Out-File "C:\input_clear.txt"

I have allready tried with -replace "'n,""" or "n,""", or "\n","" (same with r).
It replaces the spaces, but never replace the linebreaks ;o(.

PowerShell is always trying to use "'n,""" as a normal text. If i'm trying this he is using exact 'n, when it is in the text file..

How my Powershell ISE will understand 'n or 'r as a linebreak?

I'm new to powershell and this is my 2nd script.. Maybe someone could tell me what I'm doing wrong?

Thanks in advance.