Re: Low a/c airflow on first floor
There is far less cooling load on the first floor, so by design there would be less air volume serving the first floor. What you observe could be normal.
First there are all of the obvious things that need to be checked, i.e. air filters, blower and evaporator cleanliness, separated ductwork, closed balancing dampers, etc...
If the furnace or air handler is located in the second floor attic, it is not uncommon to see performance problems on the first floor, since ductwork is often "stuffed" between floor joist, cracks and crevices. This is by bar the most difficult problem to solve.
If you have a single HVAC system with two thermostats, then you probably have a zoning system, which probably utilizes a bypass damper. If the bypass damper is not working properly, then total air volume serving the home could be diminished.
Consider hiring an HVAC contractor who is ,or employs ,NATE certified technicians. They should be able to tell you what the problem is and how to fix it. Which might be pretty handy when dealing with the builder warranty (assuming there is one).
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