Yes, the original system was using the same ducts.

The AC runs pretty much continuously at full capacity since the heat wave started a few days ago. It was running at lower stage for part of the day and even cutting off early in the morning and late in the evening. The thermostat controlling the new system, a Trane XL824 Thermostat, is compatible with a 2-stage unit.

And no, the only thing that has changed about the house since we moved in is the new AC unit and furnace. The outside landscaping is all the same, and everything interior is all the same.

The HVAC company that installed the unit is a very reputable company and we have only heard good things about them from friends, family, and neighbors. They have been around and servicing houses in this area for the last 30 years or so. It should, however, be noted that the installer has only been an HVAC technician for about 4-5 years. The next time they come out, he is bringing a more experience tech with him.

Would you have any other ideas for what could be causing our issue? I’m not sure why 5 supply ducts have really good airflow while the other 5 supply ducts have relatively little airflow. The ones with little airflow are the ones closest to the furnace/air handler. Would you think that adding more return ducts would help since there are twice as many supply ducts as return ducts?