Commercial HVAC Troubleshooting

Symptom guides for rooftop units and packaged systems — cooling, lockout, and airflow problems for Puget Sound facility managers.

  • RTU & packaged systems
  • Commercial buildings only
  • Not residential DIY

Pick the symptom below that matches what you see on the roof or at the thermostat. Each guide covers likely causes and limited safe first steps only — one reset max on lockouts.

RTU

RTU not cooling

Rooftop unit not cooling your building — safe first checks for facility managers.

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RTU

High-pressure lockout

RTU high-pressure lockout — one reset max, then call for condenser airflow checks.

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Economizer

Economizer not working

Economizer stuck or wrong outside air — sensor and damper checks for commercial RTUs.

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Compressor

Compressor won’t start

Compressor won’t start on a commercial unit — electrical and control checks; 3-phase work needs a pro.

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Need repair, not troubleshooting? Commercial HVAC repair · Greater Seattle & Puget Sound

Stop now — do not troubleshoot further If any of the following apply, stop reading and act on safety first. Do not reset safety devices, bypass limits, or open gas or refrigerant lines.
  • Gas odor or suspected leak — leave the area; do not operate switches, pilots, or electrical equipment; call your gas utility or 911, then a licensed gas technician.
  • Fire, smoke, flames, or grease fire — use your site fire plan; call 911 if needed; do not restart equipment until inspected.
  • Carbon monoxide alarm or headache/nausea near gas equipment — ventilate, evacuate, and call for service.
  • Repeated high-limit, pressure, or breaker trips — one reset is not a fix; continued operation can damage equipment or cause injury.
  • Refrigerant hiss, oil stain, or suspected leak — EPA-certified technicians only; do not add refrigerant or braze lines yourself.
  • Sparking, burning smell, or exposed live conductors — shut off at a labeled disconnect if safe to reach; call a licensed technician.

Important: These guides are general information for commercial operators, not step-by-step repair instructions for untrained persons. You are responsible for following manufacturer manuals, local codes, and your insurer’s requirements. A/C Dr. Naz is not liable for injury, property damage, food loss, or code violations that result from actions taken based on this content. When in doubt, call a licensed professional.

Caution Power off at the labeled disconnect before cleaning condenser coils or reaching inside panels. Where a guide allows a single control reset, try it once only — if the fault returns, stop and schedule service.
Safe checks Thermostat setting, doors closed, visible gasket damage, ice blocking airflow, and breaker position — visual checks only, with equipment left in its normal off or on state as noted.

HVAC still down after safe checks?

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Same-day diagnostics when capacity allows · All troubleshooting categories