About the only thing I know of is the return ductwork. Check to make sure it isn't constricted or collapsed. It's just thin sheet metal. I opened ours up and inserted a 1 inch diameter tube in the center to hold the sections open. Use a lightweight PVC pipe, so it doesn't restrict the air flow. Also, check to make sure that all duct connections are tight. Check the air flow from the diffusers. An earlier unit we had didn't have one duct hooked up. Oddly enough, you will usually find the best airflow to be at the furthest diffuser away from the main unit. It's the "path of least resistance" scenario. A diffuser is "resistance" and the duct is less resistant, so the air goes all the way to the end, then exits the last diffuser with more flow than the closer one.........in MOST cases. There are always exceptions. And, remember to clean the intake filters.....often. Amazing how fast they get dirty.
