can the supply duct be too big?, say current set up for 3 ton, changed to 2 1/2 ton.
Not likely,in the senario,if it's an issue,just add a damper or other restriction to raise the static.
The ductwork may have been undersized for the 3-ton unit.
The half-ton less is inconsequential, & may improve operating efficiency.
When one gets to the larger 3.5 to 5-ton equipment, doing whatever is necessary toward downsizing tonnage is very important, so that the duct system won't be undersized!
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