Why Isn’t Your Commercial Packaged Unit Working? Tony’s Fast Diagnostic Checklist for Cooling & Heating Failures
When a 6–10 ton commercial packaged unit stops cooling or heating, business owners usually panic:
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“The dining room is roasting — fix it now!”
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“The office is freezing; the heater won’t turn on!”
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“My rooftop unit is running but no air is coming out!”
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“Our gym smells hot — is something burning?”
Tony has answered thousands of these calls.
And here’s the truth he gives every owner:
Commercial failures almost always come from predictable causes — and usually from neglect, bad airflow, or a previous cheap installation.
This blog is Tony’s field-tested diagnostic checklist — the same one he trains techs with. It covers every real cause of cooling/heating failure in 6–10 ton commercial packaged units, in the same order Tony checks them on job sites.
If your commercial HVAC is failing, start here.
1. First Step: Identify the Category of Failure
Commercial rooftop units fail in only five categories:
✔ Airflow failure
✔ Cooling failure
✔ Heating failure (gas, electric, or heat pump)
✔ Electrical/control failure
✔ Mechanical failure (rare but serious)
Tony always diagnoses by category FIRST — never by guessing.
2. Airflow Failure — The Most Common Cause of All Commercial Problems
If airflow drops, everything else collapses.
Symptoms:
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warm supply air
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low airflow
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blower loud but weak
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cold/hot spots
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coil freezing
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overheating furnace
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high energy bills
Tony’s Airflow Checklist:
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Filters clogged?
→ Replace immediately. -
Return duct undersized or blocked?
→ Most common cause in older buildings. -
Supply trunk too small?
→ Creates high static pressure. -
Blower belt loose or snapped?
→ Airflow drops to near zero. -
Blower wheel dirty or unbalanced?
→ Reduces CFM dramatically. -
Rooftop ducts leaking?
→ Heat gain kills supply temps.
Airflow FIRST — because airflow failure mimics cooling and heating failure.
*(Reference: [Commercial Airflow Failure Causes])
3. Cooling Failure — The System Runs, But No Cold Air Comes Out
Cooling issues show up most during peak daytime heat.
Cooling Failure Symptoms:
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air blowing but not cold
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unit short cycling
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compressor loud or struggling
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supply air barely cooler than return
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humidity high
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coil icing
Tony’s Cooling Checklist:
A. Dirty Condenser Coil
#1 cause of cooling failure in commercial units.
Dirty coil = high head pressure = weak cooling.
B. Frozen Evaporator Coil
Symptoms:
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weak airflow
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ice on copper lines
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water on roof
Fix:
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thaw coil
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fix airflow or refrigerant issue
C. Refrigerant Undercharge (Rare)
Tony sees this less than 10% of the time.
Usually from:
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old units
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coil corrosion
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mechanical damage
D. Refrigerant Overcharge
Caused by bad service work.
Overcharge cooks compressors.
E. Bad TXV or Stuck Metering Device
Causes:
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low suction
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erratic cooling
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coil starvation
F. Failed Outdoor Fan Motor
Compressor overheats → shuts off → warm air.
G. Compressor Issues
Signs:
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loud buzzing
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tripping breaker
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extremely high amps
If compressor fails, the unit is near end-of-life.
*(Reference: [Commercial Cooling Circuit Troubleshooting])
4. Heating Failure — Gas Heat, Electric Heat, or Heat Pump Heat Not Working
Heating issues differ massively depending on the heat type.
A. Gas Heat Failure
Symptoms:
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blower runs but no heat
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ignition clicks but no flame
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flame starts then shuts down
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strong gas smell (danger)
Tony’s Gas Heat Checklist:
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Igniter cracked or weak
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Flame sensor dirty
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Manifold pressure incorrect
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Burners clogged or rusted
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Rollout switch tripped
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Limit switch tripped
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Heat exchanger cracked (dangerous)
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Vent block or downdraft
Gas heat failure is serious — especially cracked exchangers.
*(Reference: [Safety Shutdown Standard])
B. Electric Heat Strip Failure
Symptoms:
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lukewarm air
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slow heating
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breakers tripping
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burning smell
Tony’s Electric Heat Checklist:
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Failed heat strip element
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Failed sequencer
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Incorrect voltage
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Loose wiring
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Overheating from low airflow
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Breaker undersized
Electric heat strips are simple — but expensive to run.
*(Reference: [Performance Diagnostic Manual])
C. Heat Pump Heating Failure
Symptoms:
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cold air during heating
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unit won’t defrost
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reversing valve clicking repeatedly
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frost on coil
Tony’s Heat Pump Checklist:
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Reversing valve stuck
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Outdoor coil frozen
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Bad temperature sensor
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Frequent defrost cycles
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Low refrigerant
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Outdoor fan weak
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Bad compressor staging
Heat pumps often fail from airflow or outdoor coil issues — not refrigerant.
*(Reference: [Commercial Heat Pump Heating & Defrost Failure Guide])
5. Electrical & Control Failures — Tony’s Fastest Diagnoses
Electrical failures can stop a 10-ton unit instantly.
Symptoms:
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system dead
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intermittent operation
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breaker trips
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burning smell
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thermostat blank
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stage 1 runs but stage 2 doesn’t
Tony’s Electrical Checklist:
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loose wiring
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failed contactor
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blown fuses
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bad capacitor
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failed transformer
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low voltage
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incorrect phase rotation (3-phase)
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thermostat miswired
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economizer control failure
Controls are the brain of the unit — one sensor failure can shut everything down.
6. Mechanical Failures — Rare but Expensive
Mechanical failures usually mean the system is at the end of life.
Mechanical Failure Signs:
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compressor locked
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blower motor seized
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blower wheel shattered
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cracked heat exchanger
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refrigerant leak in coil
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burned wiring from short
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cabinet rust-through
When Tony sees these, he usually recommends replacement — not repair.
7. Economizer Failures — The Hidden Reason for Cooling Complaints
Economizers cause 40% of commercial cooling issues, but business owners never suspect them.
Signs of a bad economizer:
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pulling hot outside air
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humidity high
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indoor temps won’t drop
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dampers stuck open
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noisy airflow
Tony checks:
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outdoor air damper
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mixed air sensor
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actuator
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linkage
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minimum position
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barometric relief
Owners often pay thousands in cooling bills because a $150 actuator failed.
8. Rooftop Issues: Wind, Rain, Sun & Structural Problems
Sometimes the HVAC system isn’t the issue — the roof is.
Rooftop problems that mimic HVAC failure:
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leaking curb
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rusted duct transitions
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wind-driven downdrafts
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hail-damaged coils
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UV-damaged wiring
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water pooling around unit
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negative building pressure from kitchen exhaust
Tony always inspects the surrounding roof area — NOT just the unit.
*(Reference: [Weather Impact Assessment])
9. Tony’s Rapid Failure Diagnosis Flowchart
Here’s Tony’s real-world “5-Minute Rule” for diagnosing commercial HVAC:
Step 1: Check airflow
90% of problems start here.
Step 2: Check cooling/heating output
Measure temps and pressures.
Step 3: Check electrical components
Contactors, fuses, sequencer, transformer.
Step 4: Check controls
Thermostat wires, economizer, sensors.
Step 5: Check mechanical components
Compressors, motors, exchangers.
This rule solves 95% of on-site failures in under 30 minutes.
10. Tony’s Final Verdict: Commercial Failures Are Predictable — If You Know Where to Look
Here’s Tony’s no-nonsense summary:
✔ 70% of failures = airflow
✔ 20% of failures = electrical/control
✔ 7% of failures = refrigerant
✔ 3% of failures = true mechanical failure
Most failures are preventable, and most repairs are cheaper when caught early.
Commercial HVAC doesn’t die suddenly — it gives warnings.
Ignoring them guarantees breakdowns at the worst time.
Let's know how much this unit will cost in 2025 in the next blog.
