Seasonal changes present unique challenges in school environments, where HVAC systems must balance comfort, indoor air quality (IAQ), and strict budget constraints. This technical deep dive focuses on the "seasonal tactic" — a systematic, proactive approach to preparing school HVAC systems for the transition between cooling and heating seasons (and vice versa). Unlike a simple filter change, this tactic requires a thorough understanding of building automation, psychrometrics, and mechanical wear patterns. For the technician, executing this correctly prevents emergency calls, extends equipment life, and ensures compliance with ASHRAE standards.

The Seasonal Tactic: A Systematic Approach

The seasonal tactic is a structured sequence of inspections, adjustments, and preventive maintenance actions performed at the two major transition points: fall (heating season start) and spring (cooling season start). It is not a reactive repair but a deliberate, documented procedure. The goal is to identify and correct issues that develop during the off-season, such as dust accumulation on coils, actuator binding, or control calibration drift.

Pre-Season Planning and Documentation

Before touching any equipment, review the previous season's service records and any outstanding work orders. Obtain the school's HVAC schedule — many schools operate on a modified calendar with summer sessions or winter break shutdowns. Document the outdoor air temperature and humidity at the start of the procedure. This baseline is critical for later verification of economizer operation and dehumidification performance.

Critical Safety and Lockout/Tagout (LOTO)

School mechanical rooms often have multiple power sources. Verify LOTO for all disconnects — including 24V control transformers — before opening panels. Many schools have integrated fire alarm or energy management systems that can re-energize equipment remotely. Use a voltage tester on capacitors and verify zero energy state. For rooftop units (RTUs), ensure the ladder is stable and the roof surface is dry and slip-resistant.

Fall Transition: Heating Season Preparation

The fall transition is arguably more critical because it involves combustion safety and freeze protection. The primary focus is on verifying heat exchangers, gas trains, and hydronic systems are ready for sustained low-temperature operation.

Heat Exchanger Inspection and Combustion Analysis

For gas-fired furnaces, boilers, and unit heaters, perform a visual inspection of the heat exchanger using a boroscope or mirror. Look for cracks, sooting, or corrosion — especially at the tube sheet and around the burner ports. Follow up with a combustion analysis: measure oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), and stack temperature. For induced draft furnaces, verify the draft pressure switch operation and flue gas flow. Record the CO reading in the flue gas; any reading above 100 ppm (air-free) warrants further investigation and potential shutdown of the unit.

Hydronic System Checks (Boilers and Radiant Heat)

Inspect the expansion tank for proper air charge (typically 12-15 psi for a two-story school). Check the pressure relief valve by manually lifting the lever — it should reseat cleanly. Verify the low-water cutoff (LWCO) operation by draining the boiler slightly and confirming the burner shuts off. For systems with glycol, test the freeze point with a refractometer. Ensure glycol concentration is between 30% and 50% depending on local climate, and check for corrosion inhibitor levels using test strips.

Spring Transition: Cooling Season Preparation

The spring transition focuses on restoring dehumidification capacity, verifying refrigerant charge, and ensuring condensate management is functional before the first heat wave.

Condenser Coil and Air-Cooled Equipment

Clean the condenser coils thoroughly using a fin comb and a low-pressure water rinse (do not use a pressure washer — it can bend fins and damage the coil). Inspect the condenser fan blades for balance and the fan motor for bearing wear. For chillers, check the oil level and sight glass for discoloration. Verify the condenser water pump (if applicable) is primed and the strainer is clean.

Evaporator Coil and Airflow Verification

Inspect the evaporator coil for dirt, mold, or biological growth. Use a UV light to check for microbial contamination. Measure total external static pressure (TESP) across the supply and return plenums. Compare to the manufacturer's blower table. High static pressure indicates a dirty coil, undersized ductwork, or a restricted filter. Adjust blower speed if necessary to achieve the design airflow (typically 350-400 CFM per ton for schools).

Refrigerant Charge and Superheat/Subcooling

With the system running in cooling mode, measure suction pressure and liquid pressure. Calculate superheat and subcooling using the appropriate refrigerant type (R-410A is most common in newer schools, but R-22 is still present in older units). For TXV systems, target superheat is 8-12°F and subcooling is 10-15°F. If readings are out of range, check for refrigerant leaks using an electronic leak detector. Do not simply add refrigerant — recover and weigh the charge if necessary.

Controls and Economizer Verification

School HVAC systems often rely on economizers to bring in free cooling during mild weather. A malfunctioning economizer can waste energy and cause IAQ problems.

Economizer Actuator and Damper Operation

Cycle the economizer through its full range of motion. Verify the minimum position setpoint (typically 10-20% for schools) is maintained during occupied mode. Check the mixed air temperature sensor and the return air temperature sensor for accuracy. Use a psychrometer to compare readings. If the economizer is equipped with a CO2 sensor for demand-controlled ventilation (DCV), verify the sensor calibration and response time.

Thermostat and Sensor Calibration

Check all zone thermostats and space temperature sensors against a calibrated thermometer. Many schools have wireless sensors that can drift over time. Recalibrate or replace sensors that are more than 2°F off. Verify the occupancy schedule in the building automation system (BAS) matches the school's current calendar. A common mistake is leaving the system in "unoccupied" mode during a teacher workday, causing discomfort.

Common Mistakes and How to Avoid Them

Even experienced technicians can make errors during seasonal transitions. The following list highlights the most frequent pitfalls.

  • Skipping the condensate drain check: A clogged drain causes water damage and IAQ issues. Use a wet/dry vacuum or compressed air to clear the primary and secondary drain lines. Pour a cup of water into the drain pan to verify flow.
  • Overlooking the filter rack seal: A gap around the filter allows unfiltered air to bypass, fouling the coil and reducing efficiency. Use a flashlight to inspect the filter rack seal and replace gaskets if necessary.
  • Assuming the gas valve is off: Always confirm the gas supply is shut off before servicing gas trains. Use a manometer to verify zero pressure at the inlet.
  • Ignoring the outdoor air intake: Leaves, debris, and bird nests can block the intake. Inspect and clean the intake screen and bird screen.
  • Failing to document the transition: Without a written record, the next technician (or the school's facilities manager) has no baseline. Use a checklist and take photos of critical readings.

When to Call a Senior Technician or Inspector

Not all issues can be resolved during a routine seasonal tactic. Recognize the signs that require escalation.

Combustion Safety Concerns

If the combustion analysis reveals CO levels above 200 ppm (air-free) after burner adjustment, or if a heat exchanger crack is visible, shut down the unit immediately and call a senior technician. Do not attempt to weld or patch a cracked heat exchanger — it must be replaced.

Refrigerant Leaks and Circuitry Issues

If you suspect a refrigerant leak in a system with multiple circuits or a chiller, call a senior technician with recovery equipment and nitrogen. Do not attempt to braze a leak without proper evacuation and pressure testing. For systems with R-22, a senior technician can advise on retrofit options or drop-in replacements.

Electrical and Control Panel Faults

If you encounter a burned contactor, a shorted transformer, or a control board with visible damage, stop and call a senior technician. These faults can indicate underlying issues like phase imbalance or transient voltage. A senior technician can perform a power quality analysis.

Structural or Code Violations

If you find asbestos insulation on pipes, improper flue venting, or missing fire dampers, contact the school's facilities manager and the local building inspector. Do not proceed with work that could disturb asbestos or create a fire hazard.

Tools and Equipment for the Seasonal Tactic

Having the right tools ensures efficiency and accuracy. The following list covers the essential items for a school seasonal transition.

  1. Combustion analyzer (with O2, CO2, CO, and stack temperature sensors)
  2. Electronic leak detector (for both R-22 and R-410A)
  3. Psychrometer (digital or sling) for wet-bulb and dry-bulb measurements
  4. Manometer (for gas pressure and static pressure)
  5. Boroscope or inspection mirror for heat exchanger and coil inspection
  6. Refractometer (for glycol freeze point)
  7. Fin comb and coil cleaner (non-acidic for aluminum coils)
  8. Multimeter with temperature probe (for sensor calibration)
  9. LOTO kit (padlocks, hasps, tags, and voltage tester)
  10. Documentation forms (checklist, photos, and a tablet or clipboard)

Practical Takeaway

The seasonal tactic is not just a checklist — it is a disciplined, data-driven process that protects the school's investment and ensures occupant comfort and safety. By systematically addressing heating and cooling transitions, you reduce emergency service calls, improve energy efficiency, and build trust with school administrators. Always document your findings, escalate when necessary, and treat each transition as an opportunity to fine-tune the system for the months ahead. For further reading on best practices, consult ASHRAE Standard 62.1 for ventilation and IAQ, and the EPA's IAQ Tools for Schools program for comprehensive guidance.