I've got an 8 year old Comfortmaker AG042GB 42,000 BTU with a 10.4-11.5 SEER rating. The evaporator is U42PC22A1 with an 078 restrictor according to the label. The furnace is a Comfortmaker GUK100N16C1.
I've always had to keep the house quite cool (72 or lower) in order to keep the humidity below 60%. My suspicion is that the A/C is oversized. The house is a 2000 square foot two story and well insulated (R50 attic, R15 walls, triple pane low-e Pella windows). The house is also well shaded. Additionally the house is about 1/2 mile inland of Lake Michigan wich reduces outside temperatures 6-8 degrees vs. the surrounding area but doesn't reduce the humidity.
The air conditioning normally runs about 5 minutes per cycle.
I realize that accurate sizing requires detailed calculations beyond what can be done here.
Mainly what I'm trying to do is to become a bit more knowledgeable before I start talking with contractors. After reading this forum for a while I've seen a few options other than replacing the air conditioner with a smaller unit:
Don't use the continuous fan setting
Slow the blower down
Replace the restrictor with a TXV and slow the blower more
Get a high capacity dehumidifier
I already have a small (40 pint rating) dehumidifier in the basement.
The furnace blower was on the highest speed (factory default) tap. I've changed the blower speed tap to a lower setting and may have gotten a minute or so extra run time.
Any other ideas?