"Out of Memory" Error due to Excel not releasing memory

I import sheets into a file, then save the file with a new name in a different location.

The macro works until the memory usage for Excel reaches about 3,000MB, at which point an "Out of Memory" error occurs. (There is 32GB of memory on this PC.)

The error occurs on this line, Set Wkb3 = Workbooks.Open(filename:=Path & "\" & filename) presumably because there isn't enough memory to open another file.

Wkb3, which is the source file where the sheet is being imported from, is closed after the import.

Wkb2, which contains the collection of imported sheets is saved and closed after the imports are done.

Wkb1 is the only one that is constantly open.

I usually manage to go through 40 or so iterations before the crash, so clearly even though all Wkb2 and Wkb3 are being closed, something is staying in Excel's memory.

I tried saving Wkb2 after each import to see if that will release memory.

I tried setting Objects to nothing.

Here's my macro:

Option Explicit
Sub CombineFiles()
Call NewBook 'this marco creates a new file that will hold the imported sheets

Dim Wkb1 As Workbook 'Wkb with Macro
Set Wkb1 = ThisWorkbook

Dim Aname As String
Aname = Wkb1.Sheets(1).Range("A1").Value & "\Master File\Master File.xlsx" 'cell A1 holds the path for each individual folder that holds files that need to be combined

Dim Wkb2 As Workbook 'MasterBook
Set Wkb2 = Workbooks.Open(filename:=Aname)
Dim Wkb3 As Workbook 'DataSource
Dim ws1  As Worksheet 'Wkb with Macro
Set ws1 = Wkb1.Worksheets(1)
Dim ws3  As Worksheet 'DataSource

Dim MyOldName As String
MyOldName = Wkb2.FullName

Dim Path As String
Path = ws1.Range("A1").Value

Dim filename As String
filename = Dir(Path & "\*.xlsx", vbNormal)

Dim Path2 As String
Dim filename2 As String
Path2 = Path & "\Master File\"

Do Until filename = ""
    Set Wkb3 = Workbooks.Open(filename:=Path & "\" & filename)
    For Each ws3 In Wkb3.Worksheets
        ws3.Copy after:=Wkb2.Sheets(Wkb2.Sheets.Count)
    Next ws3
    Wkb3.Close False
    filename = Dir()
Loop

Application.DisplayAlerts = False
filename2 = Wkb2.Worksheets(2).Range("A2").Text
Wkb2.SaveAs filename:=Path & filename & ".xlsx"
Wkb2.Close True
Kill MyOldName
Call KillFiles
Application.DisplayAlerts = True
End Sub

Unfortunately, the only fix I was able to come up with was to Kill excel and restart the Macro via the Windows Task Scheduler. It doesn't fix the "out of memory" error, but at least it restarts the Macro every now and then so I don't lose time on it being stuck on this error.

If you are running Exce32 bits, the limit is 4Gb.