Getting back to the under-performing AC. bought a used class c and was not satisfied with the ac performance. It was a ducted system with the chill grill. Lived with it for as while thinking it was what it was. I ended up having to change A-C unit on roof to get lower roof clearance for in building storage that became available.When I removed the chill-grill I found that the mid-section seals had been ripped by the PO allowing air to short circuit. I say seals but a large part of the setup was metallic duct tape. Quick to check and boy did it make a difference.