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**Why Your A-Coil Freezes Up — And Why It’s Not the Refrigerant’s Fault Most of the Time**

Tony breaks down the REAL causes of frozen coils—airflow failures, blower problems, filthy ductwork, bad installation, and everything homeowners never think about.

When an A-coil freezes, homeowners always point fingers in the wrong direction:

“It must be low refrigerant.”
“The AC needs a recharge.”
“Probably the condenser is going bad.”
“Maybe the thermostat is broken.”

Nope.
Wrong.
Way off.

**Low refrigerant is the cause in maybe 10% of frozen A-coil cases.

The other 90%?
Airflow problems, dirty equipment, and installation mistakes.**

Your Goodman CAPFA6030C3 A-coil is engineered to run cold — but NOT below freezing. When something interferes with airflow, heat transfer collapses. Without enough warm air passing over the coil, the refrigerant keeps absorbing what little heat is available… until coil surface temperature drops below 32°F.

Then it starts freezing.
Then it becomes a block of ice.
Then the system shuts down.
Then the compressor is at risk.

And if you don’t fix the REAL cause, the ice comes right back.

So today Tony’s breaking down:

what actually causes freezing
which parts of the system are responsible
the airflow science behind freeze-ups
how coils freeze even with perfect refrigerant charge
how poor ductwork kills a system
how to diagnose the freeze cause correctly
what NEVER to do when you see ice
and how a good install prevents every freeze-up

Let’s get into it — Tony style.

First: Understand HOW an A-Coil Freezes (No Fluff, Just the Real Physics)

Your A-coil freezes when:

**1. The refrigerant inside is too cold

AND
2. Not enough warm air is moving across the coil.**

That’s it.

People want complicated answers.
But it’s always those two factors.

Now here’s the part most homeowners miss:

Low airflow is responsible for MOST freeze-ups.

To keep the coil above freezing, it MUST receive:

proper airflow
proper refrigerant boiling
proper drainage
proper return air temperature

Any disruption to any of those leads to freezing.

This is the foundation of the freeze-up problem:
[Evaporator Heat Transfer Decline Leading to Coil Surface Temperature Drop]

Let’s break down ALL the causes — the real ones Tony finds in the field.

Cause #1: Dirty Air Filter (The #1 Freeze-Up Cause in the World)

This one is so common it’s almost embarrassing.

A filthy air filter suffocates your system.

When the coil doesn’t get enough airflow:

✔ refrigerant doesn’t boil properly
✔ coil temperature plummets
✔ moisture freezes instantly
✔ coil turns into an ice block

Airflow starvation is the single greatest freeze trigger.

Signs this is your issue:

filter hasn’t been changed in months
filter collapses when removed
airflow feels weak
coil freezes quickly after startup

Here’s the airflow principle behind this:
[Filter Restriction and Impact on Evaporator Coil Surface Temperatures]

A $12 filter can prevent $2,000 of damage.
Most people learn that too late.

Cause #2: Dirty A-Coil (Airflow Blockage That Sneaks Up Over Time)

Even if your filter is perfect, dust WILL accumulate on the coil over time.

A dirty coil:

✔ blocks airflow
✔ causes uneven cooling
✔ traps moisture
✔ lowers coil temperature
✔ makes icing almost guaranteed

If your coil hasn’t been cleaned in 3–5 years?
It’s filthy. Period.

Dust acts like insulation.
You wouldn’t wrap your refrigerator in a blanket and expect it to cool — so don’t do it to your coil.

Here’s the science behind dirty-coil freeze-ups:
[Reduced Airflow and Latent Heat Transfer Decline Due to Coil Fouling]

A clean coil is a cold coil.
A dirty coil is a frozen coil.

Cause #3: Weak or Failing Blower Motor (Low CFM = High Ice)

Your blower motor MUST generate enough CFM (cubic feet per minute) to keep the coil warm enough to prevent ice.

If the blower:

runs slowly
fails intermittently
is clogged with dust
has a weak capacitor
is incorrectly wired
is fighting high static pressure

…the coil loses airflow and freezes.

A faulty blower is a silent killer because the system may sound like it’s running, but airflow output is severely reduced.

Signs:

✔ weak air from vents
✔ blower slow to start
✔ blower shutting off during cycle
✔ rumbling or humming sounds

This is the blower effect explained:
[Blower Performance Degradation and Evaporator Coil Freeze Risk]

If the blower isn’t pushing the air, the coil WILL freeze — guaranteed.

Cause #4: Undersized or Restricted Ductwork (The Hidden Freeze Monster)

You could have a brand-new Goodman coil and a perfectly charged system — and still freeze solid because your ductwork is a disaster.

If your ducts are:

too small
crushed
kinked
clogged
poorly designed
leaking excessively
undersized for a 3.5–5 ton coil

…then airflow plummets.

The coil starves for warm air.
The refrigerant boils too slowly.
The coil temperature drops.
Ice forms.

This is one of the biggest reasons older homes freeze coils when upgrading to bigger equipment.

Here’s the duct airflow principle that explains it:
[Duct Static Pressure Effects on Evaporator Airflow and Freeze Tendency]

If your duct system can’t breathe, your coil can’t survive.

Cause #5: Incorrect Airflow Direction / Wrong Coil Orientation

If your coil is installed:

in the wrong airflow direction
at the wrong tilt
with a misaligned drain pan
without proper sealing
on the wrong furnace orientation

…you’re asking for freeze-ups.

Wrong orientation destroys:

✔ refrigerant distribution
✔ drainage
✔ airflow path
✔ coil temperature balance

When air moves across the coil in a direction it wasn’t designed for, the entire refrigerant pattern collapses.

This is the orientation factor:
[Evaporator Coil Malfunction Due to Incorrect Upflow/Downflow Installation]

Improper installation ruins coils — and freezing is the first symptom.

Cause #6: Low Refrigerant Charge (Yes, It Happens — But Not as Often as Homeowners Think)

Low refrigerant causes:

✔ reduced evaporator pressure
✔ colder coil surface
✔ faster freezing

But here’s the truth:

Most freeze-ups blamed on “low refrigerant” are actually due to:

airflow issues
dirty coils
blower problems
duct restrictions

A real refrigerant-related freeze-up involves:

✔ hissing coil
✔ long runtimes
✔ weak cooling
✔ ice forming slowly from the bottom up
✔ low suction pressure
✔ no improvement after filter change

But don’t assume refrigerant is the issue — it’s the minority case.

Here’s the refrigerant science behind it:
[Low Refrigerant Charge and Pressure Effects on Coil Temperature]

Always rule out airflow first.

Cause #7: Oversized Equipment (The Silent Freeze Trigger)

Bigger is NOT better.

An oversized system:

✔ cools the air too fast
✔ doesn’t run long enough to manage humidity
✔ causes moisture to cling to the coil
✔ lowers coil temperature too much
✔ triggers freeze-ups in humid weather

In other words:

“Too much cooling capacity” = a frozen coil waiting to happen.

This is especially common with:

a 5-ton coil on a 3.5-ton airflow system
a large condenser on a weak duct system
improperly matched equipment

Here’s the oversizing principle:
[Excess Cooling Capacity and Its Impact on Evaporator Coil Frost Formation]

Oversized systems freeze more than undersized ones.

Cause #8: Bad Thermostat Settings (Yes, This Happens Too)

If the blower settings or cooling stages are set wrong, the system can freeze.

Examples:

constant low-speed blower on a high-tonnage coil
dehumidify mode without proper airflow
incorrect thermostat staging
wrong CFM-per-ton settings

Smart thermostats cause more freeze-ups than people realize.

Cause #9: Blocked Condensate Drain (Water Backflow Into Coil)

When the coil drains properly, moisture leaves the system smoothly.

When the drain is:

clogged
incorrectly pitched
lacking a trap
improperly routed

…the pan fills with water.

Standing water + cold coil = ice formation.

Once ice forms, the whole coil becomes a frozen block.

Cause #10: Frozen Coil After a Power Outage or Long Off-Cycle

When the system restarts:

refrigerant pressures haven’t equalized
the blower may kick on before the coil temp normalizes
moisture left on the coil instantly freezes

This is less common, but Tony sees it enough to mention.

What You Should NEVER Do When Your Coil Is Frozen

Homeowners always make these mistakes — and Tony wants to save you from yourself.

❌ DO NOT run the system with the ice still on the coil

You will destroy the compressor.

❌ DO NOT chip the ice off manually

You will puncture the coil.

❌ DO NOT “add refrigerant” blindly

You will flood the compressor.

❌ DO NOT switch to heat without checking the blower

You may overheat the furnace.

❌ DO NOT assume the problem is gone once the coil thaws

It’ll freeze again within hours.

Let the coil thaw with the system OFF and diagnose the cause.

How Tony Diagnoses a Frozen Coil (The Field-Proven Method)

Here’s EXACTLY how Tony identifies the freeze cause:

✔ Step 1 — Check the air filter

If dirty → FIX that FIRST.

✔ Step 2 — Check blower motor speed, capacitor, cleanliness

If airflow is weak → FIX that second.

✔ Step 3 — Check coil cleanliness

Dirty coil = freeze.

✔ Step 4 — Check duct static pressure

High static = freeze.

✔ Step 5 — Check refrigerant pressures

Only AFTER airflow is confirmed healthy.

✔ Step 6 — Check coil orientation and installation

If wrong → freeze city.

✔ Step 7 — Inspect drain pan and condensate path

If backed up → freeze.

✔ Step 8 — Inspect metering device

A stuck TXV or wrong piston will freeze the coil.

Tony never jumps to refrigerant.
Airflow FIRST.
Always.

Signs Your Freeze-Up Is NOT a Refrigerant Problem

If ANY of these are true, refrigerant is NOT the cause:

✔ AC cools well before freezing
✔ coil freezes quickly
✔ blower sounds weak
✔ filter is old
✔ drains are clogged
✔ coil is dirty
✔ duct system is undersized
✔ coil orientation is incorrect
✔ blower shuts off mid-cycle

These ALL point to airflow.

Tony’s Final Verdict

Frozen coils are almost NEVER the equipment’s fault.
They’re the result of:

✔ bad airflow
✔ dirty coils
✔ weak blowers
✔ wrong coil orientation
✔ bad ductwork
✔ clogged drains
✔ poor installations
✔ oversized systems
✔ wrong thermostat settings

Only about 1 in 10 freeze-ups come from actual refrigerant leaks.

So stop blaming the refrigerant.
Stop blaming the condenser.
Stop thinking the AC “just needs a recharge.”

Fix the airflow.
Fix the installation.
Fix the ductwork.

Do that — and your Goodman CAPFA6030C3 coil will stop freezing FOREVER.

Drain pan and condensate issues will be discussed in the next blog.

Tags: Tony’s toolbox talk