Do you mean A/C unit on top? If so, is the roof sagging where the unit is mounted? Stretch a length of string across the roof using a helper and see if there is a gap by the A/C. I believe the factory just cuts a hole in the roof and installs the unit as well.
My old pup carried 5 bikes plus a metal bike rack on the roof with no issues.
2006 23B Hybrid with 10k round bar WDH
2011 F150 4x4 SCREW Ecoboost, Max Tow, Integrated TBC, 3.73 LS axle, Firestone Ride Rite airbags.