Key Takeaways
- Start with simple checks: power, thermostat, breakers, and filters.
- Some fixes are safe for building staff (reset breakers, clear drains, replace filters).
- Refrigerant, compressor, and major electrical faults require licensed technicians.
- Know warning signs that demand immediate professional help to protect people and property.
Common Symptoms
- Complete loss of cooling or heating
- Unit runs but delivers weak or no conditioned air
- Unusual noises (clicking, grinding, loud hums)
- Repeated tripping of breakers or blown fuses
- Water pooling under or near equipment
- Hissing or oily residues suggesting refrigerant leaks
- Burning smells, smoke, or visible sparks
Possible Causes & Solutions
Power or Control Circuit Failure
How to Identify: Check circuit breakers and main disconnects for tripped positions. Verify the unit's service switch is ON and the thermostat has power and correct mode. Look for blown fuses or loose control wiring at the rooftop or mechanical room panel.
Solution: Reset tripped breakers and replace blown fuses with correct type. Ensure thermostat settings are correct and fresh batteries installed. Tighten visibly loose control wires only after turning off power. If breakers trip again or wiring looks burned, turn power off and call a pro.
DIY: Yes
Clogged Air Filter or Restricted Airflow
How to Identify: Inspect supply and return filters — dirty, dusty, or blocked filters restrict airflow. Check supply and return grilles for obstructions and confirm blower fan is running.
Solution: Replace or clean filters per manufacturer specifications. Remove obstructions and ensure grills are open. If the blower fan is not operating but power is present, do not disassemble the motor — call a technician.
DIY: Yes
Condensate Drain Blockage/Overflow
How to Identify: Look for water pooling around the indoor unit or drip pans, and check the condensate pan and drain line for standing water. Many systems have a float switch that shuts the unit off when the drain is blocked.
Solution: Turn off unit power, clear visible debris from the drain pan, and use a wet/dry vacuum on the condensate drain access or outdoor drain line to remove clogs. Flush the line with water and a small amount of diluted bleach if permitted by local code. Restore power and monitor.
DIY: Yes
Refrigerant Leak or Low Refrigerant
How to Identify: Symptoms include reduced cooling capacity, iced evaporator coils, hissing sounds, or oily residue near line sets and service ports. Compressors may run continuously without achieving setpoint.
Solution: Do not attempt to add refrigerant unless you are certified. Seal obvious oil-wet areas to slow migration and limit system run time to prevent compressor damage. Contact a licensed HVAC technician for leak detection, repair, and proper recharge per EPA rules.
DIY: No - Professional recommended
Compressor or Major Mechanical Failure
How to Identify: Loud knocking, high-pitched squeal, burning smells from the compressor area, or the outdoor unit not running while indoor fans do. Repeated hard starts or no-start conditions are signs of compressor issues.
Solution: Isolate power to the unit and contact an experienced commercial HVAC technician. Compressor replacement or major mechanical repairs require specialist tools and refrigerant handling.
DIY: No - Professional recommended
Condenser or Evaporator Fan Motor Failure
How to Identify: Outdoor or indoor fan not running while other components have power. You may hear a humming sound or intermittent operation. Visual inspection can show broken blades or seized bearings.
Solution: If the fan is blocked by debris, remove debris with power off and test. Motor replacement, capacitor replacement, or bearing work should be handled by a technician. A temporary measure is to turn off the affected unit until repairs are made to avoid compressor overheating.
DIY: Yes
When to Call a Professional
Call a licensed commercial HVAC technician immediately if you detect burning smells, smoke, refrigerant leaks, repeated electrical failures, or standing water that risks property damage. These scenarios indicate hazardous conditions or failures that can worsen quickly and may require specialized tools, refrigerant recovery, electrical diagnostics, or component replacement. For non-life-safety issues where building operations are affected (critical server rooms, pharmaceutical storage, kitchens), contact emergency HVAC services as soon as basic checks are completed. Keep the system powered off if you observe sparks, smoke, or severe mechanical failure, and arrange for a professional assessment to avoid further damage or safety risks.
Frequently Asked Questions
How fast should an emergency HVAC technician respond?
Response times vary by provider and time of day, but commercial emergency services typically respond within 1-4 hours for critical systems. For mission-critical spaces (data centers, medical facilities), request priority service and inform the dispatcher of the facility’s critical needs.
Can I run a commercial HVAC unit with a blocked condensate drain temporarily?
Running a unit with a blocked condensate drain risks overflow, water damage, and mold. If you must keep the system on briefly, place a temporary external drain bucket under the pan and monitor closely, but arrange for immediate clearing of the drain or professional repair.
Is refrigerant handling a DIY job?
No. Refrigerant handling, leak detection, and recharging are regulated tasks requiring certified technicians. DIY attempts can cause injury, environmental harm, and legal violations. Limit site staff action to conserving the system and documenting symptoms for the technician.
What temporary measures can reduce downtime before repair?
Switch zoning to unaffected systems, increase ventilation with fans, relocate critical loads when possible, and perform basic checks (filters, breakers, thermostats). Communicate with occupants and prioritize areas for temporary cooling solutions like portable units.
How can I prevent commercial HVAC emergencies?
Implement a preventive maintenance program with seasonal inspections, filter changes, coil cleaning, drain service, refrigerant checks, and electrical testing. Regular maintenance catches small issues early and reduces emergency repairs and downtime.