Choked Air: Diagnosing Airflow Problems in Your 5-Ton R-32 AC and Gas Furnace System

🛠️ Tony’s Hello: When Your System Can’t Breathe, Nothing Works Right

Alright, let’s just say it—when it comes to comfort, airflow is king. I don’t care how efficient your furnace is or how perfectly charged your R-32 AC condenser might be—if the system can’t move air properly, it’s toast. Doesn’t matter if it’s heating or cooling. Poor airflow means uneven temps, short cycling, noise complaints, high energy bills, and calls from frustrated homeowners wondering why their “brand new system” still doesn’t feel right.

I’ve been on so many service calls where the system looks good on paper—matched equipment, clean filters, even a new thermostat. But you dig a little deeper and find the blower speed is set wrong, static pressure is off the charts, or someone shoehorned a 5-ton unit into ductwork meant for a 3-ton setup.

So today, I’m going to walk you through everything I know about diagnosing airflow problems in these 5-ton R-32 combo systems. Whether you’re installing new or fixing an underperforming setup, I’ve got the tools, tricks, and tests you need to get it breathing right. Let’s clear the path and let that air flow. 🧢

 

📐 Start with Sizing: Is the System Matched to the Ductwork?

One of the biggest mistakes I see with 5-ton systems is mismatched ductwork. A 5-ton unit moves around 2,000 CFM of air, give or take. That means your supply and return ducts have to be sized to handle that flow, or you’re gonna run into bottlenecks and pressure issues.

Here’s a rough rule of thumb:

• 400 CFM per ton of cooling = 2,000 CFM for 5 tons

• Return duct should be at least 20 inches wide if round or 24x10 if rectangular

• Supply trunks must be balanced with branch takeoffs that don’t restrict flow

Need a deeper dive on duct design? The Manual D from ACCA is still the industry gold standard for residential duct sizing.

If you’re working with existing ducts in a retrofit, it’s worth checking the friction rate and duct velocity—undersized ductwork is the silent killer of high-efficiency systems.

 

🔧 Blower Motor Settings: ECM vs PSC and How They Move Air

Most Goodman 5-ton furnaces, like the GR9T961205DN, come with ECM variable-speed motors, which are smarter than the average blower but still need to be set up right.

Here’s what I look for during setup:

• Match the blower tap settings to your cooling tonnage and external static pressure

• Make sure the cooling airflow (CFM) is set to 400 CFM per ton unless the manual calls for more or less

• For gas heat, double-check that the heating airflow is appropriate for your BTU rating

If you’re new to ECM motors, Goodman has a setup guide, which explains dip switch settings and troubleshooting.

And if you’ve got an older PSC motor? It might be time for an upgrade. PSCs can’t adjust airflow on the fly, and they tend to struggle with static pressure increases.

 

📏 Measure Static Pressure: Your Airflow Blood Pressure Test

You want to know how your system’s really doing? Check the static pressure.

Total external static pressure (ESP) for most residential systems should be under 0.5” WC. Anything higher, and you’re choking your airflow. Here’s how I check it:

• Drill test ports before the coil and after the blower

• Use a reliable manometer like the Testo 510 or Fieldpiece SDMN6

• Add supply and return pressure readings to get total ESP

ASHRAE explains static pressure’s impact on system performance in more detail.

If your pressure’s high? Start looking at the usual suspects:

• Dirty filters

• Undersized returns

• Blocked ducts or closed dampers

• Coils full of dust and pet hair

 

🌀 Filter and Coil Blockages: The Usual Suspects

If the blower’s working hard but airflow’s weak, your filter or coil is likely the problem.

Start with the filter:

• Use a MERV 8 or 11 for residential use—MERV 13 is great, but not without duct mods

• Check for collapsed or bypassing filters

• Replace regularly (every 60–90 days in most homes)

Next, the coil:

• Dirty indoor coils are a common problem, especially in homes with pets

• Check for condensation leaks pooling in the pan

• Use a non-acidic coil cleaner and rinse thoroughly

The Department of Energy backs this up—dirty coils are one of the top causes of poor performance and short cycling.

 

🚫 Duct Leaks, Crushed Runs, and Flex Duct Fails

Flex duct is great for quick installs, but it’s notorious for being installed badly. I’ve seen more crushed runs, unsupported spans, and lazy takeoffs than I care to admit.

Here’s my flex duct checklist:

• Limit flex duct runs to 6 feet or less whenever possible

• Always support every 4 feet with straps

• Avoid tight bends, kinks, and pancake layouts

• Seal all joints with mastic or UL-181 tape

And don’t forget to check returns! I’ve diagnosed so many systems with “bad airflow” that just had a disconnected return boot sucking attic air.

The Building Performance Institute has great guidance on duct testing and sealing practices.

 

🌬️ Balancing the Airflow: Dampers, Registers, and Room Pressure

Sometimes the system is moving enough air overall, but the distribution is off. That’s when you get hot rooms, cold rooms, and “dead zones”.

Here’s what I do to fix it:

• Adjust dampers at the takeoffs or in-line to balance flow

• Use anemometers at registers to verify CFM

• Add manual dampers in long runs when needed

• In two-story homes, try blending airflow between floors for better stability

And don’t ignore door undercuts. If a room closes off and becomes pressurized, it’ll struggle with return airflow. Sometimes all it takes is installing transfer grilles or jumper ducts.

 

🔍 Diagnosing Airflow Issues Like a Pro

Here’s my step-by-step process when I walk into a home with airflow complaints:

1. Ask the homeowner what rooms feel uncomfortable

2. Check return filter and verify CFM needs (400 per ton)

3. Measure total ESP with a manometer

4. Inspect coil and blower compartment

5. Walk the duct system and look for obvious damage or leaks

6. Use a static pressure chart to estimate actual CFM

7. Rebalance registers and add dampers if needed

Sometimes it’s not the unit—it’s the delivery system. Don’t just slap a charge on it and go. Take the time to walk the house and read the clues.

 

🧠 Wrapping It Up with Tony

I’ve said it a thousand times—you can have the best equipment in the world, but if your airflow’s bad, the system will never perform. It’ll be noisy, inefficient, and wear itself out long before its time.

So take your time. Measure everything. Don’t guess at duct sizing or blower speeds. Clean those coils, adjust the dampers, and always check your static pressure before you leave. That’s how you keep a 5-ton system running smooth and quiet.

And if you’re just getting started or looking for a fully matched system that plays nice with high airflow needs, the team over at The Furnace Outlet has a great lineup of Goodman 5-ton R-32 AC and gas furnace combos. These systems are built to handle high-capacity airflow, and they come with the manuals, parts, and documentation you need to set it up right the first time.

Having some issues with error codes with your 5-ton system? Visit my guide: Blinking Lights and Beeping Boards.

That’s it from me for now. Go chase that airflow, listen for the hiss in the ductwork, and remember—when in doubt, measure it out.

Catch you out there,
Tony the Trusted Tech 🧢