This combination is 9k+18k+18k (45k) on a 36k condenser. Is that kind of overhead really acceptable?

This particular combination has been approved by the manufacturer- MRCOOL. It is acceptable, in approved combinations, that the total sum of air handlers exceeds that of the condenser as long as the difference is not exceedingly large. About this system the brochure states, "If all indoor units (handlers) run simultaneously, their combined BTU output will not exceed the BTU rating of the outdoor unit (condenser)." For more information on acceptable combinations, please review page 3 of this system's brochure. The brochure can be found on the product's page with the specifications under the resources section. For more assistance, please give us a call.