How To Change One Condition Based On Another

I have a "if" statement that goes something like this:

=if(and(Function1),do this, if(and(Function2), do that, 0)

where Function 1 and Function 2 consist of three conditions each.

Now Function 2 has reference to a particular cell (U23), whose value is dependent on other cell references.

If U23 has some real value, I want the above statement to be executed.

However, if U23 displays a "#N/A", I want only Function1 to be executed. i.e. = if(and(Function1),do this,0)