🌦️ Introduction: A 3-Ton Coil Isn’t Just a Cooler — It’s a Moisture Machine
Most homeowners think their AC system’s job is simple:
“Blow cold air.”
But Tony — 35+ years in the field, thousands of Goodman and CAPTA coil installs — says that’s the wrong way to look at it.
A 3-ton AC system doesn’t cool first. It dehumidifies first, then cools.
Tony’s real quote:
“Temperature lies. Humidity tells the truth.”
And here’s the kicker:
A 3-ton coil only removes humidity correctly when the airflow (CFM-per-ton) is tuned specifically for your home’s climate, ductwork, and coil type. Get the airflow wrong — even by 10–15% — and the coil stops acting like a dehumidifier and starts acting like a noisy, inefficient air mover.
This is why Tony says:
“If you run every 3-ton unit at 400 CFM per ton because the manual says so, you’re already wrong.”
This article breaks down the real, field-proven rules Tony uses to tune airflow so your 3-ton coil behaves exactly like the dehumidifier your home desperately needs — especially with SEER2 coil restrictions.
3 Ton 15.2 SEER2 80,000 BTU 96% AFUE Goodman Upflow Air Conditioner System
🌀 1. What a 3-Ton Coil Actually Does (Most Installers Don’t Know This)
Before cooling the air, the coil must:
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Drop humidity
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Reach dew point
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Maintain coil saturation temperature
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Pull moisture off the fins
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Drain condensation effectively
A coil that isn’t cold enough doesn’t dehumidify.
A coil that’s too cold freezes.
Perfect dehumidification happens in a narrow window — usually at coil temps between 38°F and 46°F.
That temperature depends almost entirely on:
➡️ Airflow (CFM)
➡️ Refrigerant feed stability (TXV)
➡️ Indoor wet bulb temperature
➡️ Outdoor ambient temperature
Out of these four, airflow is the only one you can control directly — which is why Tony obsesses over CFM-per-ton.
✔️ AC humidity basics (EPA): https://www.epa.gov/indoor-air-quality-iaq
📉 2. Why High CFM Kills Dehumidification (and Your Comfort)
Most manuals say “400 CFM per ton” but Tony says that’s outdated for:
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SEER2 coils
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High static duct systems
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High humidity homes
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Multi-stage equipment
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Modern tighter houses
High airflow:
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Warms the coil
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Increases coil temperature
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Reduces latent capacity
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Removes less moisture
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Causes “cold but sticky” comfort
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Forces longer run times
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Raises indoor humidity to 60–70%
Tony calls this:
“The Florida problem — cold house, wet house.”
With today’s restrictive coils like the CAPTA series, 400 CFM/ton often pushes the coil into sensible-only cooling, meaning it cools but does not dehumidify.
And humidity = discomfort.
❄️ 3. Why Low CFM Causes Coil Freeze (and Compressor Damage)
On the flip side:
Too little airflow:
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Drops coil below freezing
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Causes frost on the bottom
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Then freeze across entire face
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Chokes airflow further
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Floods refrigerant back to compressor
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Can destroy scroll compressors
Tony’s rule:
“If you see frost, don’t reach for your gauges — check your airflow first.”
✔️ Coil freeze mechanics:
https://www.energy.gov/energysaver/maintaining-your-air-conditioner
🌍 4. Tony’s CFM-per-Ton Rules by Climate Zone
Tony sizes airflow based on humidity and house load, not textbook numbers.
He breaks the country into zones:
🌵 1. Dry Climates (Arizona, Nevada, West Texas)
Target: 400–425 CFM per ton
For a 3-ton system: 1,200–1,275 CFM
Why?
Dry air → little latent load → need higher sensible capacity.
This gives:
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Faster temp pull-down
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Higher airflow comfort
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Better coil temp stability
🌤️ 2. Mixed Climates (Midwest, Carolina Piedmont, Mid-Atlantic)
Target: 360–400 CFM per ton
For a 3-ton system: 1,080–1,200 CFM
Why?
Balanced sensible + latent load.
This is Tony’s “start here” setting, then tune up or down based on real-world ΔT.
🌧️ 3. Humid Climates (South, Gulf Coast, Northeast Coastal)
Target: 320–350 CFM per ton
For a 3-ton system: 960–1,050 CFM
Why?
Humid homes need lower airflow for better moisture removal.
Tony says:
“A 3-ton coil at 350 CFM/ton will kick humidity’s butt.”
This is where the coil truly behaves like a dehumidifier.
✔️ Moisture load guidelines (EnergyStar): https://www.energystar.gov
🌡️ 5. The Truth: You Cannot Use Factory ECM Airflow Tables as-is
Modern ECM blower tables assume:
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Perfect ductwork
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Perfect static pressure
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Perfect refrigerant charge
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Perfect return paths
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Correctly sized filter racks
Tony says:
“Show me a house that perfect — I’ll wait.”
Instead, the ECM blower hits LESS airflow than the table shows because:
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Static pressure is too high
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Filters are undersized
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Returns are restricted
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Coils are restrictive (especially SEER2)
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Blower ramps down automatically
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Installed ESP is double the lab ESP
This is why Tony’s airflow tuning is done with:
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Static pressure readings
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Real ΔT
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Wet bulb readings
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Coil temperature clamp
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Amp draw
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Suction line temp
Not what the manufacturer’s table says.
✔️ ECM blower behavior explained: https://www.ahridirectory.org
🔧 6. How Tony Tunes a 3-Ton System to Behave Like a Dehumidifier
This is Tony’s exact field process.
Step 1 — Measure Total External Static Pressure
He checks:
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Return
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Filter rack
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Coil
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Supply
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Duct layout
Anything above 0.7 in. w.c. = airflow loss.
Step 2 — Set Initial CFM/Ton Based on Climate
Tony starts with:
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350 CFM/ton (humid)
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375 CFM/ton (mixed)
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415 CFM/ton (dry)
Step 3 — Check Temperature Split (ΔT)
He looks for:
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18–22°F (ideal)
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22–24°F = airflow low → increase blower
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16–18°F = airflow high → lower blower
ΔT is the truth detector.
Step 4 — Check Coil Temperature
Coil should sit:
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38°F–46°F for proper dehumidification
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Below 34°F → freeze risk
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Above 48°F → poor moisture removal
Step 5 — Adjust Blower Until Coil Acts Like Dehumidifier
That means:
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Long run cycles
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Slow, steady airflow
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Strong latent removal
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Proper drainline flow
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45–55% RH indoors
Tony’s quote:
“Set airflow for humidity, not temperature — the temperature will follow.”
🧊 7. How Wrong CFM-per-Ton Causes Stupid Comfort Problems
Tony sees these complaints every week:
❌ “My house is cool but feels sticky.”
Airflow too high.
❌ “The AC works but never catches up.”
Airflow too low — coil freezing or starved.
❌ “The AC runs too long.”
CFM-per-ton incorrect → poor latent removal → system works harder.
❌ “The air feels warm coming out of the vents.”
Airflow too low → coil freezing → ΔT collapsing.
Tony’s response:
“Comfort problems are usually airflow problems.”
✔️ Comfort & humidity guidelines (DOE):
https://www.energy.gov/energysaver/air-conditioning
🛠️ 8. The 3 Biggest Mistakes Installers Make (Tony Sees These Daily)
❌ Mistake #1 — Running 400 CFM/Ton for Every System
This kills dehumidification in humid climates.
❌ Mistake #2 — Ignoring Static Pressure
If static is 0.9+ → you will NEVER achieve rated airflow.
❌ Mistake #3 — Using 1" Filters on SEER2 Systems
A 1-inch filter can choke a blower down 15–30% airflow.
Tony says:
“If your filter rack is too small, your coil is already crying.”
🧪 9. Real-World Case: The 3-Ton System That Couldn’t Beat Humidity
A Gulf Coast homeowner called Tony:
“It’s cool, but we’re sticky all day.”
Tony finds:
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Airflow: 1,250 CFM (415 CFM/ton)
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Coil temp: 52°F
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ΔT: 15°F
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Indoor humidity: 69%
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Static pressure: 0.82"
The coil was useless as a dehumidifier.
Tony’s fix:
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Lowered blower to 1,050 CFM
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Fixed return duct choke
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Installed 4" media filter
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Lowered CFM-per-ton to ~350
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Re-set TXV bulb
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Rechecked ΔT (21°F)
Humidity dropped from 69% → 48% in 24 hours.
Tony’s comment:
“Coil didn’t need Freon.
It needed AIR CONTROL.”
🏁 Conclusion: A 3-Ton Coil Is a Dehumidifier First — Treat It Like One
Modern SEER2 coils require precise airflow tuning to deliver:
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Proper humidity control
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Correct ΔT
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Full latent capacity
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Quiet airflow
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Coil frost protection
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Maximum comfort
Tony’s final rule:
“If you tune airflow for temperature, you’ll miss.
If you tune airflow for humidity, you’ll nail it every time.”
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In the next topic we will know more about: The Return-Air Triangle — Why You Need Three Paths, Not One, for a Quiet and Balanced System
