Troubleshooting Common Issues in Large Packaged Units

🏢 1. Introduction – Why Troubleshooting Skills Save Time & Money

When a 6–10 ton commercial packaged unit stops doing its job, your building notices—fast.

• Tenants complain.

• Utility bills spike.

• In extreme weather, operations can grind to a halt.

Having basic troubleshooting knowledge:

• Cuts down on unnecessary service calls.

• Helps you relay accurate info to HVAC pros.

• Lets you fix small problems in-house before they snowball.

That said—troubleshooting a large packaged unit is not about guessing. It’s about safe, methodical testing.

---

⚠ 2. Safety First

Before touching the unit:

• Lockout/Tagout (LOTO): Shut off and lock power at the disconnect. Attach a tag so no one flips it back on.

• Wear PPE: Gloves, safety glasses, and in some cases fall protection for rooftop units.

• Refrigerant Safety: Use gauges rated for the refrigerant type (R-410A, R-454B, etc.). Avoid venting refrigerant—it’s both illegal and dangerous.

• Gas Safety: For furnace-equipped units, shut off gas at the supply valve before working on combustion components.

Jake’s rule: If you’re not licensed for gas or refrigerant work, limit yourself to inspections and basic fixes.

---

❄ 3. Cooling Problems

A. Unit Not Cooling At All

Likely Causes:

• Tripped circuit breaker

• Blown control fuse

• Thermostat not calling for cooling

• Contactor not engaging

• Low-pressure switch open due to refrigerant loss

Steps:

1. Check thermostat mode and setpoint.

2. Inspect breaker/fuses.

3. Listen for contactor pull-in.

4. If contactor is engaged but compressor/fan aren’t running—check capacitor and motor.

---

B. Poor Cooling Performance

Likely Causes:

• Dirty condenser coils

• Clogged air filter

• Low refrigerant charge

• Worn compressor

• Economizer damper stuck open

Steps:

1. Inspect coils for dirt/debris—clean if needed.

2. Replace air filter.

3. Check superheat/subcooling against manufacturer specs.

4. Inspect economizer operation.

---

C. Short Cycling (Cooling)

Likely Causes:

• Oversized unit

• Thermostat placed in poor location

• Refrigerant imbalance

• Faulty low-pressure control

Steps:

1. Observe cycle length—should be several minutes, not seconds.

2. Check thermostat placement (avoid drafts/heat sources).

3. Verify refrigerant pressures.

---

🔥 4. Heating Problems (Gas Furnace Models)

A. No Heat

Likely Causes:

• Igniter failure

• No gas supply (closed valve, empty tank)

• Limit switch open

• Faulty flame sensor

Steps:

1. Confirm gas valve is open.

2. Reset limit switch if tripped.

3. Test igniter resistance.

4. Clean flame sensor with fine emery cloth.

---

B. Insufficient Heat

Likely Causes:

• Dirty burners

• Low gas pressure

• Heat exchanger issues

• Blocked vent

Steps:

1. Inspect burner flame (should be blue, steady).

2. Measure manifold pressure.

3. Check vent/flue for blockages.

---

C. Uneven Heating

Likely Causes:

• Duct leaks

• Zone damper failure

• Blower belt slipping

Steps:

1. Inspect ducts for damage.

2. Test damper actuator operation.

3. Tighten/replace blower belt.

---

⚡ 5. Electrical Issues

A. Unit Won’t Start

Likely Causes:

• Tripped breaker

• Control transformer failure

• Thermostat wiring fault

Steps:

1. Reset breaker (if it trips again, investigate short).

2. Measure transformer secondary voltage.

3. Check for 24V signal at contactor.

---

B. Frequent Breaker Trips

Likely Causes:

• Overamping fan or compressor motor

• Short circuit in wiring

• Bad capacitor causing hard starts

Steps:

1. Measure amp draw on each motor.

2. Inspect wiring insulation.

3. Test capacitors with meter.

---

C. Intermittent Operation

Likely Causes:

• Loose wire connections

• Failing relays

• Faulty control board

Steps:

1. Tighten all terminal screws.

2. Tap suspect relays—if operation changes, replace.

3. Look for burn marks on board.

---

🌬 6. Airflow & Duct Issues

Common Symptoms: Low airflow, uneven temperatures, noise in ducts.

Likely Causes:

• Collapsed or blocked ductwork

• Dirty filter

• Blower motor failure

• Belt misalignment

Steps:

1. Check filter.

2. Measure static pressure.

3. Inspect ducts for obstructions.

4. Verify blower speed setting.

---

💧 7. Water & Drainage Problems

A. Water Overflow Inside Building

• Clogged condensate drain line

• Missing or broken trap

• Rusted drain pan

Steps:

1. Clear drain line with nitrogen or vacuum pump.

2. Verify trap is installed and functional.

3. Replace damaged pans.

B. Frozen Evaporator Coils

• Low airflow (dirty filter, blower issue)

• Low refrigerant charge

Steps:

1. Inspect and correct airflow issues.

2. Check refrigerant pressures.

---

📑 8. Creating a Troubleshooting Log

Why it matters:

• Helps track recurring faults.

• Makes vendor service faster & cheaper.

• Provides data for capital planning.

Log Template:

• Date/time

• Symptom description

• Steps taken/tests performed

• Results & readings

• Resolution or next action

---

🛠 9. Jake’s Pro Troubleshooting Tips

• Start Simple: Check the obvious before diving deep.

• Spare Parts: Keep fuses, belts, and filters in stock.

• Know Your Unit: Learn the model-specific fault codes.

• Document Everything: Today’s “minor issue” could be tomorrow’s “big problem” with a history.

• Seasonal Awareness: Summer issues often tie to cooling, winter to heating—adjust your initial checks accordingly.

In the next topic we will know more about: How Long Do Commercial Packaged AC & Gas Furnace Units Last? Lifespan & Replacement Signs