does it really make that big a difference when it comes to SEER rating
Originally Posted by cibarra
Yes and no. For starters you have an old 3 ton 10 SEER or smaller (8 or 6 SEER) older coil that cannot function well with a 3 1/2 ton outside unit. But to make matters worse the new 3 1/2 ton outside unit being a 13 SEER needs an indoor coil designed for a 13 SEER outdoor unit.
The newer 13 SEER units use a much larger indoor coil not only as part of there listing for the higher efficiency but also to offer a larger absorption area to pick up the heat and moisture off the return air that is entering the indoor cooling coil.
So two items are killing the cooling
Coil to small for the outdoor unit
Coil of different efficiency design. IE 10, 8, or 6, SEER
One of the better professionals might be able to get it working by lowering the refrigerant charge and adjusting the refrigerant flow there by shrinking the outside unit to a 3 ton per say but it will never run correctly, will use more utilities (electric) and may not last very long.
You will be better served by replacing the indoor coil with one that matches the outside unit.