Why does my door move up when I use CFrame to move down?

So I was coding a door to move down when a button was pressed. To test my code, I used a loop and a wait to control the door. But whenever I hit test, regardless of what I put in the parenthesis, the door just moves up. Does anyone know why? Thanks.

part = script.Parent
for i = 1,100 do
	part.CFrame = CFrame.new(part.Position + Vector3.new(0,-1,0))
	wait(5)
end