That line of code looks OK, check your spelling in the constant and variable assignments. I'm curious why you are assigning the constant to a variable and not using the constant directly.
This line of code is wrong : IF (nviFP_02_OSA_TEMP ) = ECONOMIZER_CONSTANT
It should look like this : IF ( nviFP_02_OSA_TEMP = ECONOMIZER_CONSTANT)
This is also incorrect in the sense that you cannot use an network variable in the code. You must assign it to a variable first
such as, nviFP_02_OSA_TEMP = OSA_TEMP