Powershell reporting wrong variable value

Your code has a few issues,

IF ($a = "True")

You cant use an = equals, you must use a -eq. Also, "True" is a String containing 4 characters, the boolean values for True and False are $true and $false, so your code becomes:

    IF ($a -eq $true)

But you can simplify this further:

    IF ($a)

Below is how i would write this logic:

if(-not (Test-Path -Path "C:\Program Files\7-Zip")){
    Write-Host "Installing 7-Zip...";
    # do stuff ... 
}else{
    Write-Host "7-Zip already installed";
}

(Like in Mathematics you start from the innermost parentheses and work outwards, in this case Test-Path -Path "C:\Program Files\7-Zip" first - which in my case returns $true. The -not() negates the result of the expression in the parentheses ( ) changing it to $false).

Given how you plan to use it, you should probably wrap it up inside a function so you can write the logic once and re-use it without duplicating the code such as:

#Simple function
function InstallIfNessersary([String] $installDir, [String] $chocoPackage){
    if(-not (Test-Path -Path $installDir)){
        Write-Host "Installing Package $chocoPackage...";
        #Do stuff with $chocoPackage
    }else{
        Write-Host "7-Zip already installed";
    }
}

#Call the function for each app
InstallIfNessersary -installDir "C:\Program Files\7-Zip" -chocoPackage 7zip
InstallIfNessersary -installDir "C:\Program Files\X" -chocoPackage X
InstallIfNessersary -installDir "C:\Program Files\Y" -chocoPackage Y

Which on my PC outputs:

7-Zip already installed
Installing Package X...
Installing Package Y...