Having recently moved to TN this is my first experience with having a heat pump system.
My problem is that from time to time when the unit is set to AC the main cold air return and some of the floor ducts blow out very warm and humid air. After a period it ceases doing that and appears to function normally. This does not happen all of the time. I was not aware of the floor vents doing this til the wife mentioned it. The large cold air return is a major culprit in this situation.
The home and the system are only 2 yrs old prox. The home has a crawl space and all of the ducts are in there.
I'm having trouble picturing a return air grill blowing air at all. A return will always be a vacuum. Not a pressure. Maybe a bad start capacitor on the blower motor, and its starts in reverse? from a draft????