Seasonal HVAC maintenance in schools is a high-stakes operation. Unlike residential work, a single oversight can affect hundreds of students and staff, leading to lost class days and emergency repair costs. While the core principles of heating and cooling remain the same, the institutional scale and strict compliance requirements of a school scenario introduce a unique set of pitfalls. This article breaks down the most common mistakes technicians make when executing seasonal tactics in K-12 facilities and provides a clear, actionable framework for avoiding them.

Mistake #1: Treating the School Like a Large Home

The most fundamental error is applying a residential mindset to a commercial institutional setting. A school is not a big house. Its HVAC systems are designed for zone control, variable occupancy, and integration with building management systems (BMS). Approaching a seasonal startup or shutdown with a "one-size-fits-all" checklist ignores the specific demands of a school's schedule, such as summer break, winter break, and the daily ebb and flow of students.

The "Set It and Forget It" Fallacy

Many technicians assume that once a seasonal changeover is complete—say, switching from heat to cool in the spring—the system is good until fall. In a school, this is rarely true. A sudden late-spring cold snap or an early-autumn heat wave can catch a system in the wrong mode. The mistake is failing to leave the BMS or thermostat setpoints with a wide enough deadband or failing to program a seasonal override schedule that accounts for the local climate's unpredictability.

Ignoring the Schedule

Schools often have drastically different occupancy patterns. A gymnasium might be used for a community event on a Saturday, while the administrative wing is empty. The common mistake is to apply a uniform schedule to the entire building. A proper seasonal tactic requires programming the BMS to match the specific usage calendar for each zone. Failing to do so leads to either wasted energy conditioning empty spaces or uncomfortable conditions for after-hours activities.

Mistake #2: Overlooking the "Shoulder Season" Transition

The spring and fall shoulder seasons are the most dangerous times for school HVAC systems. The classic error is performing a hard changeover—flipping the system from heat to cool (or vice versa) in a single day. This ignores the reality that mornings can be cold while afternoons are hot, or that a week of 80°F weather can be followed by a frost.

Rushing the Changeover Checklist

A proper seasonal tactic requires a methodical, multi-day transition. The common mistake is skipping intermediate steps. For example, when moving from heating to cooling season, a technician might:

  • Fail to inspect and clean cooling towers or condensers before the first call for cooling.
  • Skip the boiler shutdown procedure, leaving a hot water system pressurized and idle during a warm spell, risking thermal expansion damage.
  • Neglect to change the BMS setpoints for economizer operation, causing the system to bring in hot, humid outside air when it should be recirculating.

The correct tactic is to perform a phased transition over several days, testing each mode (heat, cool, economizer, dehumidification) individually before declaring the season complete.

Forgetting the Economizer

Economizers are a common source of seasonal mistakes. In spring, a stuck damper can bring in cold morning air, freezing coils. In fall, a failed actuator might keep the damper closed, wasting free cooling. The mistake is not testing the economizer's full range of motion and its control sequence during every seasonal changeover. A simple visual check is not enough; the technician must verify that the mixed air temperature sensor and enthalpy controller are functioning correctly.

Mistake #3: Ignoring the Airside Balance

Seasonal changes affect air distribution. In winter, the system might be heating the perimeter zones while the interior zones are already warm. In summer, the opposite is true. The common mistake is assuming the ductwork and diffusers are balanced for all seasons. They are not.

Static Pressure Drift

As filters load up over a season, static pressure changes. When a technician changes all filters during a seasonal startup, the static pressure drops dramatically. This can cause VAV boxes to lose control, leading to overcooling or overheating in specific rooms. The mistake is not re-checking the static pressure setpoint on the VFD or supply fan after a filter change. A 20% drop in static pressure can cause the entire airside system to operate inefficiently.

Zone Temperature Reset

Many school HVAC systems use a supply air temperature reset schedule based on outside air temperature. The common mistake is failing to adjust this schedule during a seasonal changeover. For example, a winter reset schedule might target a 55°F supply air temperature on a 30°F day. If that same schedule is left in place for a 70°F spring day, the system will struggle to maintain comfort. The technician must verify that the reset schedule matches the current season's design conditions.

Mistake #4: Neglecting the Water Side

Hydronic systems in schools—chilled water, hot water, and condenser water—are often the most neglected during seasonal transitions. The mistakes here are usually about water chemistry and system isolation.

Freeze Protection for Chillers

A common spring mistake is draining a chiller's evaporator barrel without properly purging the system of air, or failing to add the correct amount of glycol for the next winter. Conversely, a common fall mistake is assuming the glycol concentration from last year is still adequate. The correct tactic is to test the freeze point of the water/glycol solution in all hydronic loops during both the spring and fall changeovers. Do not rely on last year's test results.

Boiler Summer Shutdown

When shutting down a boiler for the summer, the mistake is simply turning off the gas and leaving the water in the system. This leads to corrosion, sludge buildup, and legionella growth. A proper seasonal tactic includes:

  1. Performing a wet layup by treating the water with a nitrogen blanket or a chemical inhibitor to prevent oxygen corrosion.
  2. Closing all isolation valves to prevent the boiler from being inadvertently fired during a summer cooling call.
  3. Documenting the boiler's state (pressure, temperature, water chemistry) for the fall startup.

Failing to do this can result in a boiler that is full of rust come October, requiring a costly acid flush or replacement.

Cooling Tower Winterization

In colder climates, winterizing a cooling tower is a critical seasonal tactic. The common mistake is draining only the basin and assuming the piping is empty. Water trapped in the spray nozzles, fill media, or supply headers can freeze and crack the tower. The correct procedure involves blowing out all lines with compressed air and verifying that the tower's heat trace (if installed) is functional. A frozen cooling tower is a catastrophic failure that can shut down an entire school's cooling system for weeks.

Mistake #5: Poor Documentation and Communication

A seasonal tactic is only as good as the information passed to the next shift or the next season. The most common mistake is failing to document what was done, what was found, and what was left undone.

The "Verbal Handoff" Trap

Relying on a verbal report to the head custodian or a note on a clipboard is a recipe for disaster. The correct tactic is to create a formal seasonal changeover log that includes:

  • Date and time of each step.
  • Setpoints before and after the change.
  • Filter condition and MERV rating.
  • Water chemistry test results (pH, glycol concentration, inhibitor levels).
  • Any alarms or faults cleared.
  • Any deferred maintenance items.

This log should be stored in the school's maintenance management system and a physical copy left with the building engineer or head custodian. Without this, the fall startup technician will have no baseline to work from.

Failing to Coordinate with School Staff

The seasonal tactic must be communicated to the school's administration. A common mistake is performing a shutdown or startup without notifying teachers or the front office. For example, a technician might shut down the boiler on a Friday afternoon, not realizing that the school has a weekend event. The correct tactic is to send a brief email or work order notification to the school's designated contact at least 48 hours before the work begins, outlining the expected impact on comfort and any areas that will be affected.

Mistake #6: Ignoring Indoor Air Quality (IAQ) During the Transition

Seasonal changeovers are prime moments for IAQ problems to surface. The mistake is focusing only on temperature control and ignoring humidity, ventilation, and filtration.

The "First Day of School" Odor

When a school is closed for summer, the HVAC system is often run in a "unoccupied" mode with minimal ventilation. When the system is switched to occupied mode for the fall startup, the first blast of air can carry dust, mold spores, and stale odors into classrooms. The mistake is not running the system in "purge" mode for 24-48 hours before students arrive. This means running the supply fan at full speed with 100% outside air (if conditions permit) to flush out the building.

Humidity Control in Shoulder Seasons

In spring and fall, outdoor humidity can be high while the cooling load is low. A common mistake is allowing the system to satisfy the thermostat without dehumidifying. This leads to high indoor humidity, condensation on cold surfaces, and mold growth. The correct tactic is to verify that the system's dehumidification sequence is active during the shoulder season. This might mean overriding the cooling setpoint to run the compressor longer or enabling a reheat cycle.

When to Call a Senior Tech or Inspector

Not every problem can be solved with a seasonal checklist. Knowing when to escalate is a critical skill. A technician should call for backup in the following scenarios:

  • BMS Communication Failure: If the building management system is not responding to commands or is showing erroneous data across multiple zones, a senior controls technician or the system integrator should be contacted. Do not attempt to re-wire a BMS controller without proper training.
  • Refrigerant Leak on a Large Chiller: A leak on a centrifugal or screw chiller is not a simple fix. These systems require specialized recovery equipment, leak detection procedures, and often a factory-trained technician. Attempting a DIY repair can void the warranty and violate EPA regulations.
  • Structural Damage to a Cooling Tower or Boiler: If a cooling tower basin is cracked or a boiler's heat exchanger is corroded, this is a safety and liability issue. A senior tech or a structural inspector must assess the damage before any seasonal startup proceeds.
  • Persistent Water Chemistry Issues: If the water tests show high conductivity, low inhibitor levels, or biological growth that cannot be corrected with standard chemical treatment, a water treatment specialist should be called. Ignoring this can lead to system-wide corrosion or fouling.
  • Code Compliance Questions: If a seasonal changeover reveals that a system is not compliant with current ASHRAE 62.1 ventilation standards or local fire codes, the technician must stop work and notify the school's facilities manager. A code inspector or a mechanical engineer should review the situation before any modifications are made.

Practical Takeaway

A successful seasonal tactic for a school scenario is not about speed; it's about methodical, documented execution. Avoid the trap of treating the school like a large residence. Focus on the shoulder season transition, the airside balance, the water chemistry, and the documentation. When in doubt, escalate. A single mistake—a frozen cooling tower, a boiler full of rust, or a moldy classroom—can cost a school district tens of thousands of dollars and damage your reputation. Use a formal checklist, communicate with staff, and always verify the system's performance in all modes before leaving the site.