I have replaced 2 37 year old HVAC units with one Trane with zone dampers. I have 1700 up and another 1700 down on each zone. The upper zone runs the most. When the upper zone runs for most of the day, the exchanger starts to squeal. I can feel the air rushing out the leaks in the ductwork before the exchanger and nothing is making to the vents. I shut off the zone but let the fan run constantly, when I hear the dripping slow I restart the cooling and by then it is cooling off outside. I have been replacing the 4" filter every month and the vents are open. What else is going wrong that is causing the freezing up?
I am not a pro just a home owner trying not to get taken for a ride.

Thanks,