🛠️ The Real World Isn’t Always Plug-and-Play
No matter how well you install it, every HVAC system runs into trouble eventually. Whether it's an R-32 unit or a legacy R-410A setup, something will trip, clog, short, leak, or lock out.
If you're a homeowner, this guide will help you understand what’s going on.
If you're a tech, it might save you a callback.
This blog focuses on 3–5 ton systems—the kind found in larger residential homes, small commercial buildings, or retrofitted older homes. The problems we’ll cover span both the cooling and heating sides, with some added insight into R-32 systems (especially if you're still getting used to the A2L category).
🔍 1. System Won’t Turn On (AC or Furnace)
🧯 Potential Causes:
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Tripped breaker or blown fuse
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Bad thermostat wiring or batteries
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Blown transformer or control board fuse
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Float switch triggered by clogged drain line
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Flame rollout or pressure switch trip on furnace side
✅ First Steps:
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Check the breaker panel. Flip it off and on again.
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Replace thermostat batteries.
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Make sure the system’s condensate drain isn’t full (common in humid climates).
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On furnaces, look for blinking LED codes on the control board—check the key on the inside panel cover.
Need a reference for diagnostic codes? Here’s a great Goodman Furnace Troubleshooting Guide.
If you’re still not getting power, it’s time to open up the cabinet. Look for a blown 3A or 5A fuse on the circuit board—especially after power surges or incorrect thermostat wiring.
❄️ 2. AC Blows Warm Air
Nothing like turning on your AC in July and getting a face full of 85° air.
🧯 Common Culprits:
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Dirty air filter (classic)
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Frozen evaporator coil
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Refrigerant leak (especially on older linesets)
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Faulty reversing valve (in heat pump systems)
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Incorrect blower speed setting
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Outdoor condenser not running
✅ What You Can Do:
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Change the air filter
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Set the system to OFF and fan to ON—this helps defrost the coil
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Inspect the condenser—is the fan running? Is the unit hot or cold to the touch?
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Check for frost or ice on the copper refrigerant lines at the air handler
If you see a frozen coil, wait until it defrosts, then call in a pro. Don’t keep running the system—it can wreck the compressor.
Refrigerant leaks, especially with R-32, need licensed handling. The EPA’s Section 608 Requirements make it clear—only certified techs can recharge systems with refrigerant.
🌬️ 3. Weak Airflow
Air coming out, but barely? There’s a short list of suspects.
🧯 Common Issues:
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Dirty blower wheel
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Clogged filter or return grille
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Collapsed or disconnected ductwork
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Undersized return air
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Bad ECM or PSC blower motor
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Furnace set to incorrect fan speed tap (common in DIY installs)
✅ What to Check:
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Swap filters first
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Open every register and feel the airflow
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Look for one duct that’s totally dead—could be crushed or popped off
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If you’ve got access, inspect the blower wheel behind the furnace panel—dust cakes reduce airflow big time
If you’re comfortable using a manometer, check static pressure across the system. Many problems get blamed on the unit when it’s really a duct design issue.
Check out HVAC School’s guide to static pressure for a deep dive.
🔥 4. Furnace Not Igniting
If your gas furnace runs the blower but doesn’t fire up, the problem’s usually in one of three places:
🧯 The Big Three:
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Flame sensor is dirty
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Pressure switch is stuck open
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Ignitor is cracked or burned out
✅ What to Do:
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Remove and clean the flame sensor with a Scotch-Brite pad
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Check the vent pipe outside—is it blocked by debris or birds?
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Listen for the inducer fan to spin up. If not, the board might not be sending voltage
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Use a multimeter to test continuity on the ignitor—but only after it's cooled off
If you’ve got error codes blinking, match them to your furnace manual. Here's a reference from Carrier’s troubleshooting guide.
Keep in mind: If it tries to light 3 times and locks out, it’s probably a sensor or gas valve issue—not just airflow.
🧊 5. Condenser Fan Not Running
This one’s sneaky because everything inside looks fine—but the outdoor unit is dead.
🧯 Usual Suspects:
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Failed capacitor (classic bulge or leaking oil)
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Bad fan motor
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Contactor is stuck or burned
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No 24V signal to the coil due to thermostat or board issue
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High-pressure switch tripped due to airflow or overcharge
✅ How to Handle It:
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Check the capacitor with a multimeter (or just replace it if you’re unsure—it’s a cheap fix)
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Inspect the contactor—if it’s pitted or won’t pull in with 24V applied, replace it
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If the fan won’t spin freely, the motor might be locked up
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Make sure the system hasn’t overheated from blocked airflow or dirty coils
Don’t poke around in the contactor unless the breaker is OFF—240V will mess you up bad.
Want to learn capacitor testing in detail? This guide from HVAC School explains it perfectly.
🧊 6. R-32 Refrigerant Issues: Special Considerations
R-32 is more efficient but needs to be treated with respect. If you're troubleshooting a system that seems short on refrigerant or behaving erratically, keep this in mind:
🧯 Unique to R-32:
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It’s A2L, so leak detection is critical
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It’s a single-component refrigerant, meaning there’s no glide—good for recharging
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Slightly higher pressures than R-410A, so don’t use 410A assumptions
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Requires dedicated gauges and tools, not old 410A kits
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Charging must be done by weight, not pressure
If your system is low on charge, find the leak first. Topping off without a proper test is a recipe for disaster.
Want an in-depth R-32 safety guide? Check out this technical bulletin from ASHRAE.
🧰 7. When to Call a Pro
Some homeowners are confident with multimeters and screwdrivers, and that’s great. But here’s where you draw the line and call in a licensed HVAC tech:
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Refrigerant work of any kind
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Control board or low-voltage issues you don’t fully understand
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Combustion analysis or gas pressure checks
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Electrical troubleshooting inside a 240V cabinet
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Anything involving warranty work—doing it yourself can void coverage
🧩 System Is Short-Cycling (Turns On and Off Rapidly)
This can happen on both heating and cooling sides and usually points to one of the following:
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Thermostat location issue (too close to return)
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Oversized equipment (yes, even new ones)
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Dirty coils
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Low airflow
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Overcharged system
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Faulty flame sensor or pressure switch (on furnace)
You’ll need to do a full system check including:
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Temp rise (furnace)
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Superheat/subcooling (AC)
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Static pressure
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Thermostat delay settings
Short-cycling eats up energy and wears parts out fast. It’s one of those “fix it now, or pay a lot more later” issues.
🔗 The R-32 Systems Built for Easy Diagnostics
If you’re running a matched modern system, you’re already ahead of the game. That’s why I recommend starting with proven gear like the 3–5 Ton R-32 AC and Gas Furnace Systems. They’re designed for straightforward maintenance, smart diagnostics, and long-term efficiency.
🧤 Jake’s Final Word: You Can’t Fix What You Don’t Understand
I’ve walked into so many service calls where the last guy just swapped a part and crossed his fingers. That’s not troubleshooting—that’s guessing.
If your system is down, stay calm:
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Listen for strange sounds
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Look at LED codes
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Change the filter
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Feel for air at every register
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Don’t jump to conclusions—start with the basics
And when in doubt, call a tech who knows R-32 and works clean. It’s not about throwing parts at a problem—it’s about diagnosing it right the first time.
Whether you're a DIYer, new tech, or homeowner trying to keep cool, this guide gives you a head start—and probably saves you a few hundred bucks too.
— Jake Lawson
Field Tech | HVAC Detective | Owner of Way Too Many Multimeters
