VB.NET Custom classes?

I have this class in my project:

Class PointType
Public X As Double
Public Y As Double
Public Z As Double
End Class

I create two PointType Objects like this:

Dim tempWorldPointB As PointType
Dim tempWorldPointA As PointType

tempWorldPointB = New PointType
tempWorldPointA = New PointType

tempWorldPointB.X = 1
tempWorldPointB.Y = 2
tempWorldPointB.Z = 3

This works

tempWorldPointA.X = tempWorldPointA.X
tempWorldPointA.Y = tempWorldPointB.Y
tempWorldPointA.Z = tempWorldPointB.Z

Why does this not work?

tempWorldPointA = tempWorldPointB
I do not get an error but the values become zero.

Lines like the following are within a loop and work the first time but not after

tempWorldPointA.X = tempWorldPointA.X

tempWorldPointA.Y = tempWorldPointB.Y

tempWorldPointA.Z = tempWorldPointB.Z

tempWorldPointA = tempWorldPointB

What error do you get?

I think it may be because 'tempWorldPointA' has no value from what I can see. It has 3 seperate values for X,Y,Z but not as 'tempWorldPointA'.