Hey folks, Mark Callahan here.
I’ve been on more rooftops and crawlspaces than I care to count, and let me tell you—nothing frustrates techs and homeowners alike more than a brand-new Goodman system throwing high head pressure errors right after install. If you’re dealing with a 3 Ton 14.5 SEER2 R-32 system—specifically the GLXS4BA3610 condenser paired with the AMST36CU1300 air handler—this guide is for you.
Let’s cut the noise. This isn’t about topping off refrigerant until the numbers “look right.” This is about doing it by the book—safely, accurately, and in line with manufacturer guidelines. That’s how you avoid callbacks and compressor issues down the line.
Step 1: Understand What “High Head Pressure” Actually Means
Before you even crack open your tool bag, get your head around what we’re dealing with.
High head pressure (also called discharge pressure) happens when your system’s compressor is working too hard to move refrigerant through the condenser coil. It’s usually caused by one of the following:
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Overcharged refrigerant
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Dirty condenser coil
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Restricted airflow
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Non-condensables (like air or moisture) in the lines
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Incorrect DIP switch settings on the air handler
For a deeper dive into refrigerant system pressures, I recommend this no-nonsense technical explainer from BuildOps.
Step 2: Check the Obvious First
Let’s not skip the basics. Before you even touch the manifold:
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Check condenser coil cleanliness – A layer of dirt acts like a blanket.
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Verify fan direction and speed – Make sure it’s blowing upward and pulling air correctly.
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Inspect the filter and indoor coil – You’d be surprised how often airflow is restricted at the air handler.
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Measure line set length – Is it within Goodman’s spec (usually 25–50 ft standard, up to 150 ft with adjustments)?
Still seeing high head pressure? Now we dig into the refrigerant side.
Step 3: Use Subcooling—Not Just Pressure—to Check R-32 Charge
Here’s where people mess up. You don’t charge R-32 systems based on pressure alone. It’s all about subcooling.
What’s Subcooling?
Subcooling is the difference between the saturated condensing temperature and the liquid line temperature. For R-32, it’s the safest, most accurate way to confirm proper charge.
What You’ll Need:
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Digital manifold gauges that support R-32
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Temperature clamp (on liquid line)
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Manufacturer specs for target subcooling
For the GLXS4BA3610, you’re usually looking for 10°F to 12°F of subcooling, but always verify with the data sheet that came with your unit.
✅ For more on the importance of subcooling in R-32 systems, check out this resource from Number Analytics.
Step 4: The Right Way to Check and Adjust the Charge
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Run the system in cooling mode for 10–15 minutes until it stabilizes.
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Measure liquid line temperature with your clamp.
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Read saturated condensing temp from your gauge’s R-32 scale.
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Subtract the two to get your subcooling value.
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Compare it to Goodman’s specs.
If it’s too low? Add R-32 in small increments (always liquid, never vapor with R-32). Too high? You’re overcharged—recover refrigerant, don’t just dump it.
⚠️ Safety Reminder: R-32 is an A2L mildly flammable refrigerant. Wear gloves, eye protection, and use UL-listed tools rated for A2L refrigerants. Need more? HVAC Know It All breaks it down well here.
Step 5: Verify DIP Switch Settings
This one trips up a lot of folks. The air handler (AMST36CU1300) uses DIP switches to control blower CFM. If these aren’t correctly set for your tonnage, airflow will suffer—and so will head pressure.
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For a 3-ton system, you need 400 CFM per ton, so set the DIP switches to 1200 CFM.
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Refer to the Goodman install manual or this DIP switch guide from CE if you’re unsure.
Step 6: Double-Check Line Set Insulation and Sizing
Improper line set sizing and poor insulation can throw off refrigerant performance and cause your system to run hot.
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3/8" liquid line and 3/4" suction line is standard for 3-ton units, but check install conditions.
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Replace deteriorated or sun-baked insulation—especially on the suction line.
You’ll find a detailed walkthrough of proper line set sizing here on HVAC School.
The Final Word from Mark
When your Goodman R-32 system is screaming with high head pressure, don’t guess. Don’t touch that charge until you’ve checked airflow, cleaned coils, and verified your DIP switches. Then—and only then—check subcooling the right way using the correct tools.
This is a precision system, not a backyard window unit. If you treat it like one, you’ll be back on-site again next week.
Need a solid R-32 Goodman 3 Ton 14.5 SEER2 system to install right the first time? Start with this unit from The Furnace Outlet—it comes ready to roll with factory match specs:
👉 Goodman 3 Ton 14.5 SEER2 R-32 System – GLXS4BA3610 + AMST36CU1300
Worried about installation mistakes? Visit: How to Avoid Them on Your Goodman GLXS4BA3610 + AMST36CU1300.
Stick to the playbook. Your compressor (and your reputation) will thank you.
- Mark, your go-to HVAC tech
