Original A/C equipment may not be performing well &, may not be undersized
We need to know a lot more about your situation.
In the NE, what large city do you live near?
Your A/C may not be undersized but rather it may not be performing near up to par.
Simple easy anyone can do ways to check the performance of your central air conditioner so, if needed; you can call an Energy Efficiency HVAC Technician. Want to find out...?
If U want us to run a ballpark analysis of how your system is performing in respect to its 'Nominal Rated Btuh' we need at least the following information & numbers:
Performance Data Collection – Best Time to collect data is late afternoon around 4:30 pm, when attic is HOT; also when outdoor temps are around 85; 95; 105F or, anywhere in between.
*All U need is a good thermometer (digital reading in tenths preferable) & and indoor Humidity Gauge
1) Helpful; Tonnage & SEER of Unit &/or outdoor condenser model number: __________________
2) TXV or, orifice metering device? _______. Only if U know…
3) Outdoor condenser’s discharge-air-temperature ______-F
Subtract Outdoor air temperature: _______
Outdoor Condenser Air-Temp-Split _______
4) Need the ‘Indoor’ percent of relative humidity - in the middle of the rooms or, at Return-Air inlet grilles ___
5) Indoor Return-Air Temperature ______
Subtract Indoor Supply-Air Temperature ______ -F
Indoor temperature-split _______-F
If U can find a turn in the small liquid line insulate the temperature-probe; get its temperature for the subcooling analysis:
Small liquid line temperature ____F
To measure return air the wet bulb temp, wrap a small/thin, wet (not dripping) piece of cloth around the probe and put it into the Return Air grille & then close to the closest Supply Air diffuser near the air handler (need air movement). Wait until the temperature stabilizes - may take a little while.
Return Air wet bulb ____F
Supply Air Wet Bulb ____F
Need the above information for troubleshooting & performance analysis.
A Goodman 2-Ton 13-SEER condenser, 800-cfm indoor airflow; 80-F indoor dry bulb & 50% relative humidity; Indoor temp-split 18 to 19-F.
@ 85-F outdoors; 103.9-F - 85-F outdoors or around an 18.9-F temp-split;
@ Indoor 75-F, 63-wet bulb around 50% RH - condenser temp-split is only around 14.9-F.