- Equipment does not fail on average days. It fails on the hottest afternoon, when every unit runs flat out and every marginal part is under its highest stress.
- The most valuable pre-summer tasks are unglamorous: clean condenser coils, verify refrigerant charge and airflow, test controls and economizers, and check electrical connections.
- Capacity falls as outdoor temperature rises. A system that holds setpoint at a mild ambient may not at the extreme, so prioritize what must stay cool and shed what does not.
- Inland and desert-adjacent sites see longer, hotter seasons and Santa Ana wind events that load coils with dust and debris. Coastal sites see fewer extremes but more corrosion.
- A written heat-event plan with trigger conditions, roles, and contacts is more useful than good intentions. Cooling centers and refuge rooms need generator-backed cooling.
- Documentation done in advance, and during the event, protects your tenants, your insurance position, and your next budget request.
Why the hottest week is the hardest on equipment
Air conditioners reject heat to the outdoors, and the hotter the outdoor air, the harder that is. As ambient temperature rises, condensing pressure climbs, compressor current rises, and cooling capacity per unit of power falls. At the same moment the building's heat gain is at its maximum, so a system that was sized with a modest margin finds that margin consumed. The result is a spiral: units run continuously, never reach setpoint, and push every component toward its limits.
Failure usually comes from the weakest link rather than the biggest component. A swollen capacitor, a pitted contactor, a belt that has been slipping for months, or a condenser fan motor running warm will survive ordinary days and give out under a heat load. Dirty coils make it worse because dirt acts as insulation and raises head pressure. When the high-pressure safety trips, the unit shuts down just when it is needed most.
The business consequences differ by building type. A retail tenant loses customers and perishable inventory. A school loses instructional days or has to modify schedules. A warehouse with temperature-sensitive goods loses product. A senior living community faces resident health risk. A restaurant loses a Friday night. Planning starts with knowing which of your spaces cannot tolerate a failure and which can.
Timing: when to start and what a realistic calendar looks like
Pre-summer work should be finished before the first sustained hot spell, not started after it. In Southern California that window varies by location: coastal areas heat up gradually and late, while inland valleys and desert-adjacent cities can see serious heat early in the season. In practice, spring is the time for inspection, cleaning, and repairs, because parts are available, technicians are less stretched, and there is time to fix problems found.
| When | Focus | Typical activities |
|---|---|---|
| Late winter to early spring | Assessment | Walk the roofs and equipment, review last year's failures, build the repair list, budget for replacements |
| Spring | Service and repair | Coil cleaning, charge and airflow verification, electrical tightening, belt and bearing work, economizer and controls testing |
| Early summer | Verification | Run units under load, confirm setpoints and schedules, test generators and alarms, brief staff on the heat plan |
| During heat events | Response | Monitor, shed load, communicate, document, dispatch |
| Autumn | Review | Debrief, update records, plan replacements while lead times allow |
Lead times matter. Replacement rooftop units and large components can take weeks or months to arrive, and crane scheduling adds to the calendar. A decision to replace an aging unit made in April may not complete before the hottest days. If the equipment is nearing the end of its useful life, our RTU guide and Title 24 permits guide describe the planning steps, and a staged plan with temporary cooling can cover the gap.
The pre-summer checklist
The items below are the ones that most often separate a building that rides out a heat wave from one that doesn't. They are written for rooftop and split-system buildings but apply broadly.
- Clean condenser coils. Wash from the inside out where possible, using appropriate cleaners, and protect surrounding surfaces. A coil clogged with cottonwood fluff, dust, or leaves can lose significant capacity.
- Clean evaporator coils and replace filters. Restricted airflow causes freezing, low capacity, and compressor stress.
- Verify refrigerant charge using measured superheat and subcooling, not a rule of thumb. Low charge means a leak that needs to be located and repaired, not simply topped off.
- Check condenser fans and motors, looking for bearing noise, blade damage, and amperage out of range.
- Inspect electrical components: capacitors, contactors, wiring terminals, and disconnects, with thermal imaging where useful.
- Check belts, sheaves, and bearings on supply and exhaust fans.
- Clear condensate drains and verify pump operation and float switches.
- Test economizers: damper movement, actuator response, sensors, and changeover logic.
- Verify thermostats, sensors, and schedules. Confirm that overrides are not left on and that setbacks do not clash with morning startup.
- Inspect ductwork and insulation for leaks and gaps that waste cooled air.
- Check roof conditions, such as curb flashing, condensate disposal, and clearance around units.
- Run each unit through a full cooling cycle and record supply and return temperatures, amperage, and pressures.
Most of these tasks are part of a competent seasonal visit. A recurring preventive maintenance program builds them in and spreads the work through the year. For buildings without a program, a one-time pre-summer service followed by a plan to keep going is a reasonable start, and the maintenance plan options show how that can be structured.
Refrigerant charge, leaks, and why topping off is a trap
Refrigerant does not get used up. A low-charge system has a leak, and adding refrigerant without finding it just postpones the failure and adds to the emissions record. On a hot day, a low-charged system struggles more than usual because the evaporator and compressor have less margin to work with, and compressors can overheat because they depend on returning refrigerant to cool the motor.
Charge should be assessed with the right instruments: gauges or digital manifolds, temperature probes at the right points, and manufacturer charging data for the system type. Correct charge depends on airflow, so filters and coils should be clean before any adjustment is made. Charging a unit with a dirty evaporator coil produces a wrong answer that looks right.
For regulatory reasons, leaks above certain system sizes have to be documented, repaired within set timeframes, and verified. The details are in our refrigerant compliance guide for California. Confirm current requirements with the relevant agencies. A pre-summer leak check on large systems is both a compliance habit and a reliability measure.
Controls, economizers, and operating strategy
Controls determine how the equipment behaves when stressed. Many facilities find that changes to schedules and setpoints made over the years have left conflicting settings. A pre-summer controls review catches those before they matter.
- Schedules. Make sure startup time gives the building time to pull down before occupancy. Starting too late on a hot day produces uncomfortable mornings and a peak load spike.
- Setpoints and setbacks. Excessive setback depth can create a recovery load the equipment cannot satisfy on a hot day.
- Staging and lockouts. Confirm that compressor stages and any outdoor-temperature lockouts operate as intended.
- Overrides. Find and remove stale manual overrides that keep equipment locked in a mode.
- Alarms. Ensure high-temperature and equipment-fault alarms reach someone who can act.
- Sensor accuracy. A sensor reading several degrees off can cause short-cycling, overcooling, or lack of cooling.
Economizers use cool outdoor air to reduce mechanical cooling when conditions allow. When they work, they save energy, and when they fail, they typically fail open or stuck, bringing hot air into the building or leaving the compressors to do all the work. A stuck-open damper on a hot day can overwhelm a unit, and a stuck-closed one may waste energy in shoulder seasons. Test the full range of movement, calibrate sensors, and review the changeover setting. Our building controls service covers this verification.
Local conditions: coast, inland valleys, and Santa Ana events
Southern California is not one climate. Coastal Orange County, Los Angeles, San Diego, and Ventura enjoy marine moderation but can be hit by offshore wind events that produce short, intense heat. Inland valleys and the Inland Empire commonly see prolonged high temperatures with warm nights that never allow equipment to rest. Desert-adjacent locations push things further. Each pattern stresses equipment differently.
| Setting | Main stress | Planning emphasis |
|---|---|---|
| Coastal | Salt air corrosion, humidity, occasional offshore heat spikes | Coil coatings, corrosion inspection, readiness for rare extremes |
| Inland valleys and Inland Empire | Long periods of high ambient, dust, warm nights | Capacity margin, coil cleaning frequency, early-season service |
| Desert-adjacent | Very high ambient and sun load, wind-driven dust | Equipment ratings at extreme ambient, shading, filtration |
| Urban heat islands | Radiated heat off pavement and roofs, restricted airflow in dense layouts | Condenser placement, recirculation of hot discharge air |
Santa Ana wind events deserve their own mention. These dry, offshore winds can bring heat to normally mild areas in autumn, when many maintenance teams have relaxed their guard, and they carry dust, ash, and debris that plug coils and filters. After a Santa Ana event, check outdoor coils, intake screens, and filters, and consider whether smoke or ash from nearby fires requires a change in outside air strategy.
Our Orange County climate guide describes how local conditions affect equipment choices and maintenance cycles in more detail, and our regional pages for the Inland Empire and other counties summarize the commercial characteristics of those areas.
Load shedding, utility programs, and cooling centers
During the worst days, the electrical grid can be strained, utilities may call for conservation, and some customers participate in demand response programs. A building that can reduce its cooling load gracefully is better placed than one that must choose between everything and nothing.
- Pre-cooling. Lower setpoints modestly in the morning, within what the equipment can sustain, so the building starts the peak with stored cooling in the structure.
- Zone prioritization. Decide which spaces must remain cool, such as server rooms, pharmacies, refrigerated storage, and resident areas, and which can float.
- Reduce internal loads. Turn off unneeded lighting and equipment, close blinds, and avoid heat-producing activities in the afternoon.
- Stagger startups after power interruptions to avoid a surge that trips breakers.
- Raise setpoints in unoccupied zones rather than shutting down entirely, to avoid long recovery periods.
- Know your utility program options and any commitments tied to them, and confirm current terms with the utility.
Some facilities, such as libraries, community centers, schools, and municipal buildings, serve as cooling centers during heat emergencies. A cooling center must actually cool, so the space chosen should have robust equipment, backup power for the cooling, reliable restrooms and water, and access for people with disabilities. If your building has a role in a local emergency plan, test it before the season, not during the event. Public-sector facilities can learn more from our pages on public agency and school HVAC procurement and schools.
Emergency response: when a unit fails anyway
Even well-prepared buildings have failures. A written response plan keeps the first hour from being wasted. The plan should live where the on-duty person can find it, and its contents should be rehearsed.
- Triage. Identify which spaces are affected and which are critical. Protect people, perishable goods, and sensitive equipment first.
- Basic checks. Verify thermostat settings, breaker and disconnect status, and obvious blockages before calling, and report what you found.
- Call the service provider with specifics: unit location, symptoms, alarms, and what has been tried. Our second opinion diagnostic is available when a problem keeps returning.
- Deploy temporary measures: portable cooling, fans, window coverings, relocated people or inventory, and propped doors only if safe and secure.
- Communicate with tenants, staff, and customers about what is happening and when to expect updates.
- Document times, readings, actions, and photos as you go.
- Follow up with a root cause, not just a part swap, so the same failure does not repeat on the next hot day.
Keep a contact list that includes your service contractor, crane or rental providers, the electrician, the landlord or property manager, and an after-hours decision maker. Know the limits of what your staff can safely do. Resetting a breaker is one thing, climbing onto a hot roof alone is another.
Roof work in extreme heat is hazardous for technicians and staff. Expect service providers to adjust work hours, take heat illness precautions, and sometimes schedule non-emergency work for cooler parts of the day.
What to document, and why it pays off
Records feel like overhead until the day they are needed. After a heat event, you may be asked by a tenant why a space was uncomfortable, by an insurer what happened to the inventory, by a board why replacement is justified, or by a regulator what was done about a leak. Documentation is the answer to all of them.
- Pre-season inspection reports per unit, with readings and findings.
- Repairs and recommendations, including what was deferred and why.
- Photos of coils before and after cleaning, damaged components, and equipment condition.
- Event logs: times of failures, temperatures, actions taken, and decisions made.
- Communications to tenants and staff.
- Cost and downtime summaries that support replacement planning.
- Refrigerant records for any additions or recoveries.
The DaVinci Portal assigns each unit a QR-coded record with its service history, readings, and photos, included with service. When a unit fails on the hottest day, the technician can pull up its history immediately, and after the event you have a chronological trail. Facilities that track failures by unit can also build a data-backed case for replacement through the processes described in our project delivery and bidding guide.
Davinci Mechanical is a commercial-only HVAC and refrigeration contractor, license CA #1083101, based in Orange County with union UA Local 250 labor. Pre-summer service, maintenance programs, and replacement planning are available for the property types we serve; see our property management and warehouse pages for examples.
Frequently asked questions
When should we schedule pre-summer HVAC service?
Ideally in spring, before sustained heat arrives. Inland sites should start earlier than coastal ones. Finishing work before the first hot spell leaves time to fix what the inspection finds.
Why does my rooftop unit stop cooling on the hottest days?
High ambient temperature raises head pressure and cuts capacity, and the building heat gain is highest at the same time. Dirty coils, low charge, failing fans, or weak electrical components commonly turn that stress into a shutdown. A full inspection and root-cause diagnosis will identify which.
Is topping off refrigerant a good fix?
Not by itself. A system that needs refrigerant has a leak, and the leak should be found and repaired. Adding refrigerant without addressing it is a temporary measure and may create compliance issues.
Do we need backup power for cooling?
It depends on the building's function. Facilities with vulnerable occupants, critical equipment, or a cooling-center role should have generator-backed cooling for the refuge areas. Confirm with your electrical engineer what the generator can support.
How can we reduce load during an extreme heat event?
Pre-cool modestly, prioritize critical zones, reduce internal loads, stagger equipment startups, and follow any utility program commitments. Raising setpoints in unoccupied areas is generally better than turning equipment off completely.
What should we document during a heat wave?
Record failure times, space temperatures, actions, communications, and photos. Together with pre-season inspection reports, these support insurance, tenant, and budget discussions afterward.
Have a site this applies to?
Davinci Mechanical is the commercial and union division of Scottish Tom's Heating & Air. Send us the equipment list or the problem and we'll tell you what we'd check first.