4-Ton R-32 AC Not Cooling Right? A Tech Shows You How to Diagnose It Like a Pro

Hey, it’s Mark again ❄️

So you just had a 4-ton R-32 system installed—or maybe it’s been running a few summers—and suddenly, something feels...off. It’s running, the thermostat clicks on, but inside your house? It’s cooler than outside, but not by much. Maybe the wife’s starting to drop hints. Or your electric bill’s screaming while the rooms stay warm.

Yeah...you’ve got a low cooling issue, my friend.

Now, diagnosing this kind of thing takes a little knowledge and a lot of common sense. Don’t worry—I’ve got both. I’ve tuned up more 4-ton beasts than I can count. Grab your multimeter, your gauges, and let’s break this down like a real tech.

 

What “Low Cooling” Really Means (And What It Doesn’t)

Here’s the thing—“not cooling” doesn’t always mean your system is failing. Sometimes, it’s working exactly as it should… under bad conditions.

Before we even get into refrigerant or mechanicals, let’s define the red flags:

• Room temps stay above the setpoint, even after hours

• Weak airflow from vents

• Coil starts freezing or has condensation

• Outdoor unit runs constantly

• Electric bills spike but comfort drops

What it’s not:

• The unit won’t turn on at all (that’s electrical).

• Thermostat is dead (check the battery or low-voltage fuse).

• One room is warm but the others are fine (probably ductwork).

Let’s chase the real problem.

 

Step 1: Check the Airflow First—ALWAYS 💨

If I had a dollar for every “low cooling” complaint caused by poor airflow, I’d be writing this from a yacht. This is where 70% of problems start.

Start simple:

• Dirty filter? Change it.

• Indoor coil clogged with dust or dog hair? Clean it.

• Fan speed too low? Adjust it.

• Ducts undersized or flex duct kinked? Fix it.

A 4-ton system moves 1600 CFM. If your ducts can’t handle that, or the blower is set to “Low,” your evaporator coil won’t get enough warm air. The coil freezes, refrigerant pressure drops, and boom—your system “isn’t cooling.”

Need help figuring out how airflow ties into system function? HVAC School’s guide to airflow is required reading for anyone serious about this.

 

Step 2: Measure the Temperature Drop Across the Coil 🌡️

This is the poor man’s diagnostic. Place one thermometer at the return grill and one at the supply closest to the air handler.

Your goal is a temperature split of 16°F to 22°F.

Less than 16°F? You’ve either got poor airflow or a refrigerant issue. More than 22°F? Possibly a restricted metering device or the coil’s freezing.

Mark’s rule:
Low split + poor airflow = fan or filter issue
Low split + good airflow = charge problem or compressor issue

Got a wireless temp probe? Even better. If not, pick up a pair from Fieldpiece—they’re the best I’ve used in the field.

 

Step 3: Check for Ice on the Coil or Lines 🧊

Look at the evaporator coil. Frosted? Iced solid? That’s bad. Also touch your suction line (the bigger copper one)—if it’s frozen or sweaty all the way back to the compressor, we’ve got trouble.

Ice can mean:

• Dirty filter

• Low blower speed

• Low refrigerant charge

• Restriction at the TXV or piston

• Overcharged system (yep, that too)

Kill power and let the system thaw before moving on. Run the fan in “On” mode only for an hour to speed it up.

 

Step 4: Hook Up Gauges and Check Pressures ⚙️

Time to connect your R-32 compatible gauges (don’t use old R-410A manifolds—safety first). Here’s what to look for:

• Suction pressure too low (typically <115 psi) = undercharged or restricted

• Head pressure too high (>450 psi) = overcharged or airflow problem

• Both low = weak compressor or internal leak

Now compare the readings to your system’s charging chart. This should be in the install manual. If you don’t have it, sites like the AHRI Directory often have model-specific specs.

Mark’s pro tip: Always check superheat and subcool, not just pressures. They tell you if refrigerant is flowing, boiling, and condensing properly.

Want a fast subcooling how-to? AC Service Tech has a great blog here.

 

Step 5: Look for Leaks or Restrictions 🚨

If your charge is low and you’re not seeing ice yet, you might have a slow leak. R-32 has a faint ether-like smell, but don’t count on your nose—get a leak detector.

Common leak points:

• Line set brazes

• Schrader valves

• Service ports

• Evaporator coil joints

• Capillary tube connections

You can also bubble test with soap solution. Want to go full pro? Add UV dye and scan with a blacklight.

If it’s not a leak, it could be a restriction:

• Clogged TXV

• Kinked liquid line

• Filter drier clogged with moisture

In that case, you’ll see normal suction pressure but the coil won’t get cold.

 

Step 6: Check the Charge—By Weight If Possible ⚖️

If you’ve confirmed airflow is good, coils are clean, and no obvious leaks exist, it’s time to verify the refrigerant charge.

Now, R-32 is charge-sensitive. Overcharging doesn’t help—it hurts efficiency and spikes pressure.

If you're replacing a component or after a confirmed leak repair, evacuate and charge by weight based on the nameplate. Don’t top off unless you absolutely must.

Use a digital scale, not a spring scale. UEi or Testo make some solid ones.

 

Other Sneaky Cooling Killers 😑

Not all “low cooling” issues are refrigerant or airflow related. Here are a few curveballs that’ll mess with your comfort:

• Thermostat calibration off – 75°F might actually be 80°F

• Return vent in a hot hallway – it’s reading the wrong temp

• Blower capacitor weak – fan doesn’t run at full speed

• Oversized system – cools too fast, doesn’t dehumidify

• Improper TXV sensing bulb placement – kills superheat control

Need a sanity check on thermostat performance? ESFI’s electrical safety and control guide is a great place to start.

 

When to Call a Pro (Even if You’re Handy)

Look, I love the DIY crowd. But when you're dealing with refrigerants—especially mildly flammable ones like R-32—you’ve got to respect the system.

Call in a licensed tech if:

• You’re not EPA 608 certified

• You suspect a refrigerant leak

• Your system won’t hold vacuum

• You can’t identify restriction points

• Pressures are wild but airflow and filters are perfect

You don’t want to cook your compressor or worse—dump R-32 into your crawlspace. Safety first, folks.

 

Mark’s Final Word 💬

So, there you have it. Diagnosing low cooling in a 4-ton R-32 system isn’t magic—it’s process. Start with the simple stuff (filters, airflow, ice), then move up to pressures and charge. And always, always, measure before you mess.

These systems are powerful, efficient, and future-ready—if you treat them right. Rush through it, and you'll be watching your energy bill rise while your living room stays lukewarm.

And if you’re still in shopping mode, check out the lineup at The Furnace Outlet’s 4-ton R-32 collection. Trust me—solid gear, fair prices, and built to handle the heat.

Curious about what tools you need to have for installing your 4-ton R-32 AC system? Visit my guide: Tools of the Trade.

Catch you next time,
–Mark, your go to tech 🧊🔧