Data Validation code too long

Hi All, we had a code in our data validaton (List) in "D" and it work well but we needed to add more code to it and I think it is to much for it to handel.

Our code that worked was;

=IF(C5="A",'AC Equipment List'!$B$6:$B$800, IF(C5="SEF",'SEF Equipment List'!$B$6:$B$800, IF(C5="E",'E Equipment List'!$B$6:$B$800, IF(C5="Damper",Dampers!$B$6:$B$800, IF(C5="FA",'FA Equipment List'!$B$6:$B$800)))))

We added this to it;

=IF(C5="RAF",'RAF Equipment List'!$B$6:$B$800

Or new code that will not work is;

=IF(C5="A",'AC Equipment List'!$B$6:$B$800, IF(C5="SEF",'SEF Equipment List'!$B$6:$B$800, IF(C5="E",'E Equipment List'!$B$6:$B$800, IF(C5="Damper",Dampers!$B$6:$B$800, IF(C5="FA",'FA Equipment List'!$B$6:$B$800, =IF(C5="RAF",'RAF Equipment List'!$B$6:$B$800))))))

Is there any way we can make this work? We would like a drop down list.