Common Cooling Season HVAC Failures & How to Prevent Them
As outdoor temperatures rise, air conditioners, chillers and rooftop units can operate for longer periods of time under heavier demand. While some minor problems can go unnoticed, they can quickly cause equipment failures. Preventative maintenance can help identify these conditions before the cooling demand arrives. Find out what’s causing common cooling season HVAC failures and how to prevent them before you need to crank the AC.
Why Do HVAC Systems Fail at the Start of Summer?
The beginning of the summer marks the start of HVAC failures since most cooling equipment has likely remained idle for most of the cooler months of the year. When the first period of hot weather arrives, the system is suddenly running for longer cycles and this increased demand can expose problems that have developed over time. Common reasons for early-summer HVAC failures include:
Deferred Maintenance
If crucial components of the unit such as the filters, coils and even electrical connections haven’t been inspected since the previous cooling season, they can cause a shutdown if there’s accumulated dirt or a worn component.
Dirty Outdoor Equipment
Debris collecting around the condenser such as leaves, pollen or grass clippings can restrict condenser airflow and reduce the unit’s ability to reject heat.
Weak Electrical Components
Capacitors, contactors, relays, wiring connections, and motors can deteriorate over time. A component may appear functional during a short test cycle but fail when subjected to repeated starts or prolonged operation.
Clogged Condensate Drains
Things like dirt and algae can build up causing blockages in the drain lines while the system is inactive. Once the evaporator starts removing moisture from the air, the drain can back up and either overflow into the building or activate a safety switch.
Low Refrigerant Charge
It’s possible that there’s been a slow refrigerant leak that went unnoticed in the winter months. Under higher temperatures, the system may start to struggle to maintain a cooler temperature.
Thermostat and Scheduling Problems
Building automation schedules, cooling schedules and occupied modes may not have been updated for the summer operations. What seems to be a unit failure might actually be an incorrect schedule, sensor reading or control setting.
Increased Building Load
Solar gain, warm outdoor air, kitchen equipment, occupants, lighting, open doors, and ventilation requirements can all increase the amount of heat and moisture the HVAC system must remove.
How Do I Prevent an Early-Summer Breakdown?
Schedule a professional inspection of the cooling-system before the hot weather starts. The service should include:
- Filter inspection
- Evaporator and condenser coil inspection
- Condensate drain cleaning
- Electrical testing
- Motor and fan inspection
- Belt and pulley inspection, where applicable
- Refrigerant-circuit evaluation
- Thermostat and sensor verification
- Airflow measurements
- Complete startup and shutdown testing
Low Cooling Output in Commercial HVAC Systems: Causes and Fixes
The source of a low cooling output can occur when a commercial HVAC system runs but can’t maintain the required indoor temperature or humidity level. This can mean there’s an issue with the airflow, mechanical or electrical components, refrigerant or connectivity to the building.
1. Dirty or Incorrect Air Filters
A dirty filter increases resistance and will reduce airflow throughout the system. This can increase the blower workload and lower cooling capacity.
Recommended fix: Inspect and replace or clean the filters according to the manufacturer’s instructions. Confirm that the filter type and efficiency rating are compatible with the system’s airflow requirements.
2. Dirty Evaporator Coil
Contaminants such as dust and grease can insulate the evaporator coil and reduce the system’s ability to absorb heat.
Recommended fix: Have the evaporator coil inspected and professionally cleaned. The technician should also identify the source of the contamination and verify that the filter rack seals properly.
3. Restricted Condenser Airflow
If the condenser coil is dirty, has a blocked intake, failed fan or bent fins, this can prevent the system from releasing the heat outside like it should.
Recommended fix: Remove any loose outdoor debris and restore the required clearance for proper operation. Have an authorized service technician clean the coil, evaluate the condenser fan and straighten damaged fins.
4. Incorrect Refrigerant Charge or Refrigerant Leakage
Having too much or too little refrigerant can reduce the cooling performance. A low charge may indicate a leak so it’s important to have it rectified.
Recommended fix: Have a certified service technician inspect the refrigerant, locate and repair leaks and verify the final charge using the equipment’s manufacturer’s procedure.
5. Blower or Fan Problems
If the belt is worn, the blower wheel is dirty, or you notice a weak motor, damaged bearing or failing variable-frequency drive, that can cause reduced airflow.
Recommended fix: Inspect the blower assembly, belt tension, pulleys, motor current, wheel cleanliness, fan speed, bearings, and control signals. Correct airflow should be verified against the equipment specifications.
6. Frozen Evaporator Coil
Ice can block airflow, preventing the coil from absorbing heat properly. Some common reasons this can happen include low airflow, dirty filters, blower problems, refrigerant issues and control faults.
Recommended fix: Shut off cooling and allow the coil to thaw safely. Do not chip away the ice or apply direct heat. Have a certified service technician identify and correct the reason the coil froze before starting the unit again.
7. Duct Leakage or Damaged Ductwork
Open seams, crushed or disconnected flexible ducts, missing insulation or incorrectly positioned dampers may allow conditioned air to escape before it even reaches occupied areas.
Recommended fix: Inspect all accessible ductwork and use approved duct sealant or metal-backed foil tape for the appropriate repairs. Replace crushed sections and restore damaged insulation if you come across any.
8. Incorrect Thermostat or Sensor Readings
If you have a thermostat near cooking equipment, sunlight or another heating source, it may not read accurately. A poorly calibrated sensor can also cause undercooling, overcooling or short cycling.
Recommended fix: Verify thermostat settings, occupied schedules, sensor location, calibration, wiring, and building automation commands.
9. Improper Outdoor-Air or Economizer Operation
If the economizer damper or excessive outdoor-air intake is stuck, it can introduce hot and humid air faster than the system can condition it.
Recommended fix: Inspect the dampers, actuators, linkages, sensors, minimum-position settings, and economizer controls, then confirm that outdoor-air quantities meet applicable design and code requirements.
10. Excessive Cooling Load
New appliances, higher occupancy, damaged insulation and open doors can cause the building load to increase, meaning a lower cooling output that isn’t caused by faulty equipment.
Recommended fix: Compare current building conditions with the original HVAC design. You may need to contact a certified service technician to complete load calculations, airflow balancing, ventilation measurements, or equipment-capacity testing.
What Are Other Common Cooling Season HVAC Failures?
Clogged Condensate Drains
Having a clogged drain can increase indoor humidity, cause water leakage or activate a float switch that will shut down cooling.
Prevention:
- Inspect drain pans and accessible piping.
- Clean drains before peak cooling season.
- Test condensate safety switches.
- Correct damaged pans and improper drain slope.
- Watch for water near indoor equipment.
Failed Capacitors and Contactors
Capacitors assist certain motors during the startup and operation of the unit while contactors control the electrical power. There are a variety of factors that can cause it to fail such as heat, age, voltage irregularities and repeated cycling.
Prevention:
- Inspect capacitors and contactors during preseason service.
- Tighten electrical connections.
- Measure motor voltage and current.
- Investigate humming, clicking, or difficult startup promptly.
- Correct short cycling before it damages other components.
Condenser Fan Failure
The unit may be unable to reject heat if the condenser fan stops. This can increase operating pressure, activate a safety control or even overheat the compressor.
Prevention:
- Keep the fan guard and coil free of debris.
- Inspect the fan blade and motor.
- Address vibration or bearing noise promptly.
- Test capacitors and contactors.
- Verify that the fan starts and reaches the proper speed.
Compressor Overheating or Failure
Incorrect refrigerant charge, fan failure, dirty condenser coils, electrical problems or prolonged operations can cause the compressors to overheat.
Prevention:
- Maintain clean coils.
- Correct airflow problems.
- Repair refrigerant leaks.
- Test electrical components.
- Investigate overload trips.
- Keep equipment operating within manufacturer specifications.
Thermostat and Building-Control Failures
It’s common for commercial HVAC systems to experience problems with zone sensors, occupied schedules, control boards, relays or building automation sequences.
Prevention:
- Review cooling schedules before summer.
- Test occupied and unoccupied modes.
- Verify sensor accuracy.
- Check alarm histories.
- Confirm correct startup and shutdown.
- Inspect dampers and actuators.
How Often Should You Service HVAC Systems During Cooling Season?
Suggested Cooling-Season Maintenance Schedule
Monthly
- Inspect filters.
- Replace or clean filters when dirty.
- Check for unusual sounds or odors.
- Look for water near indoor equipment.
- Inspect visible belts and moving parts.
- Review thermostat and building-control alarms.
- Check outdoor equipment for debris.
- Compare energy use with previous periods.
Before Cooling Season
Schedule comprehensive professional maintenance that includes:
- Coil inspection and cleaning
- Drain and drain-pan inspection
- Electrical testing
- Motor and fan evaluation
- Belt inspection and adjustment
- Refrigerant-system assessment
- Thermostat and sensor testing
- Airflow measurement
- Temperature and pressure measurements
- Safety-control testing
- Equipment startup and shutdown verification
Midseason
During midseason, it’s recommended that you have the filters checked, coils cleaned, drains cleaned and inspect the electrical parts.
Quarterly
Quarterly service may be appropriate for:
- Restaurants and commercial kitchens
- Healthcare facilities
- Schools
- High-occupancy buildings
- Industrial facilities
- Buildings with continuous HVAC operation
- Properties in dusty or high-pollen environments
- Facilities with critical temperature requirements
Cooling Season HVAC Preventive Maintenance Checklist
Tasks Building Operators Can Perform
- Check thermostat settings and schedules.
- Inspect filters regularly.
- Keep supply and return openings unobstructed.
- Remove loose debris around outdoor equipment.
- Look for condensate leakage.
- Listen for new noises or vibration.
- Monitor indoor temperature and humidity.
- Review fault codes and building automation alarms.
- Record unexplained increases in energy consumption.
- Report recurring resets or shutdowns.
Tasks for Qualified HVAC Technicians
- Clean and inspect evaporator and condenser coils.
- Measure airflow and temperature change.
- Inspect blower and condenser-fan operation.
- Check belts, bearings, pulleys, and motors.
- Tighten and inspect electrical connections.
- Test capacitors, contactors, relays, and controls.
- Inspect and clear condensate drains.
- Test drain safety switches.
- Evaluate refrigerant operating conditions.
- Investigate suspected refrigerant leaks.
- Check duct static pressure.
- Verify thermostat and sensor accuracy.
- Test economizer and outdoor-air controls.
- Confirm proper equipment startup, operation, and shutdown.
When Should You Shut Down the HVAC System?
Turn off the affected equipment and contact an authorized service technician if you notice:
- Smoke or a burning odor
- Repeated breaker trips
- Significant water leakage
- Ice on the evaporator coil or refrigerant piping
- Grinding or metal-on-metal noise
- An outdoor fan that is not operating
- A compressor that repeatedly attempts to start
- Suspected refrigerant leakage
- Overheated or discolored wiring
- Rapid cycling
- Persistent safety faults
- Severe vibration