Seasonal transitions in K-12 schools create a unique set of challenges for HVAC technicians. Unlike commercial offices or retail spaces, schools have rigid occupancy schedules, strict indoor air quality (IAQ) requirements, and a high density of occupants who are sensitive to temperature fluctuations. A poorly executed seasonal changeover can lead to comfort complaints, increased energy costs, and even premature equipment failure. This article outlines the best practices for managing the school situation during spring and fall changeovers, covering the specific procedures, safety protocols, and diagnostic steps that keep a school’s HVAC system running efficiently and reliably.

Understanding the School Situation: Why Seasonal Changeover is Different

A school building is not a typical commercial structure. The HVAC system must handle extreme load variations—from a fully occupied classroom of 30 students to an empty gymnasium—often within the same day. The seasonal changeover, which typically involves switching from heating to cooling (spring) or cooling to heating (fall), is a high-risk operation. The most common mistake is assuming the system will simply switch modes without a thorough inspection. In a school, a failed changeover can mean sending students home early or operating in a partial-heat, partial-cool mode that wastes energy and creates uncomfortable hot and cold spots.

The key difference in a school situation is the need for predictability. You cannot afford to discover a stuck valve or a failed economizer actuator on the first 90-degree day of spring. The best practice is to perform a structured, documented changeover procedure during a scheduled maintenance window—typically over a weekend or during a school break—before the season actually begins.

Pre-Changeover Inspection and Documentation

Before flipping any switches or adjusting any setpoints, a thorough visual and operational inspection is mandatory. This step is often skipped due to time pressure, but it is the single most effective way to prevent a call-back during the first week of the new season.

Review the System History and Logs

Start at the building management system (BMS) or the local controller. Review the trend logs for the previous season. Look for anomalies such as:

  • High discharge air temperatures on the cooling side, indicating a possible refrigerant issue or airflow restriction.
  • Short cycling on the heating side, which could point to a dirty filter, a faulty limit switch, or an oversized unit.
  • Economizer operation—did it fail to modulate during mild weather? A stuck economizer is a common cause of simultaneous heating and cooling.
Document the current setpoints for occupied and unoccupied modes. Schools often have different schedules for classrooms, offices, and common areas. Verify that the schedule matches the current school calendar. A common mistake is leaving the system in unoccupied mode during a teacher workday, leading to extreme temperatures.

Physical Walk-Through of Key Zones

Walk through at least one representative classroom on each floor or wing. Check:

  • Thermostat operation—ensure the sensor is reading accurately and is not obstructed by books, posters, or student projects.
  • Air diffusers and grilles—look for signs of blockage (furniture, boxes) or damage.
  • Condensate drain pans—inspect for standing water, algae, or debris. A dry drain pan in winter can harbor mold spores that get blown into the classroom when cooling starts.
This walk-through also gives you a chance to speak with the head custodian. They often know about specific problem areas that may not show up in the BMS logs.

Step-by-Step Seasonal Changeover Procedure

This procedure assumes the system is a typical school rooftop unit (RTU) with gas heat and DX cooling, or a split system with a heat pump. Adapt the steps for boilers, chillers, or VRF systems as needed.

1. Lockout/Tagout (LOTO) and Safety First

Before any work begins, ensure all power sources are disconnected. This includes:

  • Disconnecting the main electrical disconnect for the RTU or air handler.
  • Locking out the gas valve for heating systems.
  • Verifying zero voltage with a meter.
Never skip LOTO in a school. The risk of a janitor or a curious student accidentally re-energizing the unit is real. Use a personal lock and keep the key on your person.

2. Filter Replacement and Airflow Check

Filters are the first line of defense for both heating and cooling efficiency. Replace all filters, regardless of whether they look dirty. In a school, filters load up faster due to chalk dust, paper fibers, and general human activity.

  • Use the correct MERV rating specified by the manufacturer. Using a higher MERV filter than recommended can restrict airflow and cause the evaporator coil to freeze in cooling mode.
  • After replacing filters, measure the static pressure across the filter bank. Record this reading. A significant increase over the baseline indicates a ductwork issue or that the filter is too restrictive.
  • Check the fan belt tension and condition. A loose belt will reduce airflow, affecting both heating and cooling performance.

3. Cooling Mode Preparation (Spring Changeover)

This is the most critical part of the spring changeover. The system has been in heating mode for months, and the cooling components are likely dirty and potentially damaged.

  1. Inspect the condenser coil. Remove any debris, leaves, or bird nests. Use a coil cleaner approved for aluminum fins. Rinse thoroughly from the inside out.
  2. Check the evaporator coil. Look for signs of oil leaks, frost damage, or microbial growth. A dirty evaporator coil will reduce heat transfer and increase compressor run time.
  3. Verify refrigerant pressures. With the system off, check the static pressure. Then, start the system in cooling mode and record the suction and discharge pressures. Compare them to the manufacturer’s target values for the current outdoor ambient temperature. A low suction pressure with a high superheat indicates a refrigerant shortage or a restriction.
  4. Test the economizer. Manually actuate the economizer damper. It should open and close smoothly. Check the mixed air temperature sensor. A failed economizer is a leading cause of high energy bills in the spring.
  5. Inspect the condensate drain. Pour a cup of water into the drain pan. Ensure it flows freely out of the drain line. A clogged drain will cause water damage to the ceiling and can lead to IAQ complaints.

4. Heating Mode Preparation (Fall Changeover)

When switching from cooling to heating, the primary concern is the heat exchanger and the ignition system.

  1. Inspect the heat exchanger. Use a combustion analyzer to check for cracks. A cracked heat exchanger can leak carbon monoxide into the classroom. This is a non-negotiable safety check.
  2. Clean the burners. Remove dust and debris. Check the flame sensor for soot buildup. A dirty flame sensor is the most common cause of a no-heat call in the fall.
  3. Test the ignition sequence. Cycle the system through a full heating call. Watch for a smooth ignition, steady flame, and proper fan operation.
  4. Check the gas pressure. Measure the manifold gas pressure with a manometer. Adjust if necessary to match the nameplate rating.

Common Mistakes and How to Avoid Them

Even experienced technicians can fall into traps during a school changeover. Here are the most frequent errors and the best practices to avoid them.

Mistake 1: Relying on the BMS Alone

The BMS is a tool, not a diagnostic device. A sensor can fail and report a normal temperature while the actual classroom is 85°F. Always verify a sample of zone temperatures with a handheld thermometer. In a school, the thermostat location is often compromised by direct sunlight, drafts, or proximity to a computer monitor.

Mistake 2: Ignoring the Economizer

Many technicians focus on the compressor and the heat exchanger and forget the economizer. A stuck economizer that is mixing in 100% outside air on a 50°F day will cause the heating system to run continuously. Conversely, an economizer that fails to open on a 70°F day will force the compressor to run, wasting energy. The best practice is to test the economizer through its full range of motion and verify the mixed air temperature sensor is accurate.

Mistake 3: Not Documenting Setpoints

After the changeover, it is common for a teacher or administrator to adjust a thermostat, thinking it will fix a temporary comfort issue. If you do not have a record of the original setpoints, you will waste time troubleshooting a problem that was created by an occupant. Document the occupied heating setpoint (typically 68-70°F), the occupied cooling setpoint (72-74°F), and the unoccupied setback temperatures. Provide a copy of this documentation to the head custodian.

Mistake 4: Overlooking the Ventilation Requirements

Schools have specific ASHRAE Standard 62.1 ventilation requirements. During a changeover, the minimum outside air damper setting can drift or become misadjusted. Use a flow hood or a manometer to verify that the minimum outside air volume is correct for the number of occupants. Under-ventilating a classroom can lead to elevated CO2 levels, causing drowsiness and headaches.

When to Call a Senior Tech or Inspector

Not every issue can be resolved on a routine changeover. Knowing when to escalate is a sign of professionalism. Call for backup in these situations:

  • Refrigerant leak detection. If you find a low refrigerant charge and cannot locate the leak with an electronic leak detector, call a senior tech with a nitrogen setup or a thermal imaging camera. Do not simply recharge the system.
  • Heat exchanger crack. If the combustion analyzer indicates a crack, or if you visually confirm one, immediately lock out the gas valve and report it to the school administration. This is a safety hazard that requires a replacement.
  • Electrical faults. If you encounter a blown fuse or a tripped breaker that re-trips immediately, do not keep resetting it. This indicates a short circuit or a failing component. Call a senior tech to perform a thorough electrical diagnostic.
  • Structural or ductwork issues. If you find water damage around the air handler, mold growth on ductwork, or signs of pest infestation, stop the work and call the school’s facilities manager. These issues may require a specialized contractor.
  • System performance that does not match design. If the system cannot maintain the setpoint after a proper changeover, and all components appear to be working, the issue may be a design flaw (undersized unit, poor duct layout). This requires an engineering review.

Practical Takeaway

A successful seasonal changeover in a school is about preparation, documentation, and a systematic approach. Do not rush the process. Spend the extra time on the economizer, the condensate drain, and the heat exchanger. Verify your work with actual measurements, not just BMS readings. And always leave the system in a state that is safe, efficient, and documented. By following these best practices, you will reduce emergency calls, improve comfort for students and staff, and extend the life of the equipment. For further reading, consult the ASHRAE Standard 62.1 for ventilation guidance and the EPA’s Indoor Air Quality in Schools page for IAQ best practices.