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all good questions. A,C on/off cycle length in minimutes? Fan "on/off"? Temp outside?

Regards TB

When there is too much air flow, the delta t is low. Also it makes the evaporator coil not as cold as it should be. Slowing the air flow to 350-400 cfm's per ton will help the unit dehumidify better. If this is 410a refrigerant, the ideal suction pressure is 120psi, which is about a 40 degree coil temperature.

Post more information please.

What is your IWB? I am assuming it is somewhere in the middle 60's. What is the TESP? What is the fan speed set at? What is the SA and RA temps? Where is the SA duct work for second story located, inside or outisde the thermal boundary? Are there any RA grilles on the second story, if so, are they outside the thermal boundary? Where is the thermostat located? What is the R-value of the walls and attic? It does sound like there is too much airflow across the indoor coil, but I am curious to hear what some of the other operating conditions are.

I'd look at the blower speed, it might be set for 3 tons. High sensible capacity and low humidity removal would be the result. The 12 degree split also leads to this.

Make sure the condenser isn't dirty, although this normally would result in the unit not cooling enough.

Humidity issues

I have a customer that is having some humidity issues on the second floor of his home. He has a 2 ton heatpump and the square footage is around 1100 sq. ft. temp mantaines around the 72-74 degree range (100+ outside) with anywere from 11-13 degree delta tee but the humidity stays around the 60 percent range. If anybody can help it would be appreciated.