House of about 1800sf had a 2.5 ton outside unit manufactured in late 2005 that seemed to perform well when the AC was run, but did not cool the house very well.
The refrigerant line was very cold and the air being blown out of the outside unit was noticeably warm, consistent with a unit that is performing very well; but the air coming out of the supply registers never got below 59F, and the house was not cooled so well. The outside air temperature in the mid 70s and the outside unit was in the shade, and not significantly obstructed.
However, supply registers on the 1st floor level were about 2/3 blocked with sheet metal that was screwed in place, and subsequently over-painted, evidently to direct more flow to the 2nd floor.
The supply air temperature was measured at a 2nd floor register that had the best outflow.
Is such supply duct blockage likely to affect the cooling performance in such a way?
Any other theories as to the reason for this apparently odd behavior of the system?