Macro doesn`t trigger when cell value changes

[MrMyagiii]

Hi,

in Sheet1 there is a simple formula in A1 that counts totals from different sheets : =H52+'sheet2'!H51+'sheet3'!H43. The value displayed is correct, however the value won`t work with either conditional formatting or macro`s.
For example when value return from formula in A1 is 1100. I compare this will a value in B1 that is 1000, the following macro doesn`t give any results:

Private Sub Worksheet_Calculate()
If [A1] > [B1] Then
MsgBox "Teveel Act!"
End If
End Sub

Same for the conditional formatting, when i set this to =$A$1>$B$1 change to red, this doesn`t work