Jacksonville: 2,000 sq ft slab house, decent windows, attic ducts.

What's wrong:

• Oversized system: 5 tons for 2,000 sq ft in Jacksonville is excessive. ACCA Manual J load calculations typically yield ~1.5–2 tons for this size home in Climate Zone 3.
• Short cycling: 8-minute run times confirm oversizing. The unit cools too fast, never reaching steady-state dehumidification.
• Humidity issues: Single-stage systems need 15–20+ minutes to effectively remove moisture. Short cycles leave the coil too warm to dehumidify properly, causing the "sticky" feeling.

What should have happened:

1. Manual J Load Calculation: Required by IECC 2020 (Florida adopted 2020 code). This determines actual cooling load based on insulation, windows, orientation, occupancy—not square footage rules of thumb.
2. Proper Equipment Sizing: Likely 2–3 tons max. Oversizing by 2x+ is common but incorrect.
3. Two-Stage or Variable-Speed Equipment: Better humidity control and longer run cycles.
4. Duct Sealing: Attic ducts in Florida often leak 20–30%. Duct blasting and mastic sealing should accompany any replacement.

Immediate fix:

• Install a properly sized 2-stage heat pump (2.5–3 tons) with variable-speed blower.
• Add a whole-house dehumidifier if humidity remains problematic.
• Seal and insulate ductwork.

Code note: Florida Administrative Code 62-6-20 mandates ACCA Manual J/S/D for new HVAC installations. The salesman's "400 sq ft per ton" rule violates proper protocol.

The homeowner is paying for inefficiency and discomfort. A real load calc and right-sized equipment will solve both.

What’s happening: Gross oversizing. A 2,000 sq ft slab-on-grade home in Jacksonville (Zone 2A) with decent windows and attic ducts typically has a sensible load of 2.5–3 tons (Manual J). The salesman used a lazy 400 sq ft/ton rule + “cushion,” doubling the actual load.

Why it feels sticky at 74 °F:

• Runtime is 8 minutes. A properly sized single-stage system runs 15–20+ minutes per cycle at design conditions.
• Latent removal requires coil temperature below dew point for sustained time. 8 minutes isn’t enough to wring moisture out of the coil and drain it; the blower re-evaporates moisture during the long off-cycle.
• Sensible load satisfied fast → thermostat hits setpoint → compressor stops → humidity climbs. You’re cooling air, not dehumidifying it.

What should have happened (code & best practice):

1. Manual J load calculation (FBC M1401.3 / IRC M1401.3). Mandatory for permit.
2. Manual S equipment selection matching both sensible and latent capacity to the load.
3. Manual D duct design for the selected airflow (350–400 CFM/ton). Attic ducts in FL need R-8 insulation and careful sealing (FBC M1601.4.1).
4. Right-size: Likely a 2.5 or 3-ton variable-speed / two-stage system with a matching air handler. Long runtimes = real dehumidification.

Fix now (short of replacement):

• Verify airflow: 350 CFM/ton actual across the coil (measure static + fan table). Low airflow worsens latent capacity.
• Add a supplemental dehumidifier (dedicated ducted unit, not portable).
• Set thermostat “cool to dehumidify” / overcool max 2–3 °F if equipment supports it.
• Seal/insulate attic ducts (major latent gain source).

Bottom line: The installer skipped the load calc (code violation) and sold tonnage. Homeowner pays in comfort and electric bill. A Manual J today is step one.