A Hampton Roads summer is warm and humid, and a heat wave is something beyond that. When afternoons climb into the mid 90s and the humidity pushes the heat index past 105 for days at a stretch, air conditioners that were coasting begin to struggle. They struggle in predictable ways. Some of the trouble is mechanical, and some of it comes from things we all do when the house is warm, with good intentions. This post covers both kinds, along with what helps a system through a stretch of extreme heat.
What a heat wave asks of an air conditioner
An air conditioner moves heat from inside the house to the outdoor coil, where it is released to the outside air, and the hotter and more humid that air, the harder the release. Systems on the coast are sized for design conditions in the low 90s, so at 96 or 98 the equipment is working past what it was built for. Refrigerant pressures rise, the compressor runs hotter, and the unit runs without a pause while holding the house a few degrees above the set point. Meanwhile the attic, where many air handlers and ducts sit, holds 130 degrees or more, and every bit of cooled air passing through it picks up heat. A healthy system in a heat wave runs all afternoon and keeps the house livable. A system with a weakness somewhere tends to make itself known when it’s needed.
The failures that surface in heat
The first is usually the capacitor. Heat is hard on capacitors, and one that was marginal in May quits on the first 98-degree afternoon, leaving the outdoor unit humming with the fan still. Aging compressors come next, since they are running hotter and longer than at any other point in the year. A system slightly low on refrigerant, which was only inefficient in June, cannot cool at all once the heat wave arrives. Condenser coils carrying a summer’s worth of salt film and pollen cannot shed heat at 98 degrees, and the compressor overheats and shuts down on its safety. And the condensate drain, moving gallons a day out of the humid air, is at its likeliest to clog and trip the float switch. Every one of these was a routine maintenance item back in spring, and in a heat wave each is an air conditioning repair call on the busiest day of the year.
Well-meant habits that make it worse
- Pushing the thermostat down to 68. The system cools at one rate no matter what the set point says, so the lower setting only guarantees it never cycles off, which stresses the compressor and removes the pauses in which the coil drains and the system dehumidifies.
- Closing vents in unused rooms. Ductwork is designed for a certain airflow, and closing vents raises pressure in the system, reduces total airflow, strains the blower, and can freeze the coil.
- Opening windows at night. A coastal night in a heat wave is in the upper 70s with heavy humidity, and every hour the windows are open, moisture comes in that the system must remove the next morning before it can cool anything.
- Crowding or covering the outdoor unit. Shade helps a little, while a cover, a tarp, or shrubs pressed against the coil block the airflow the unit depends on.
- Running the oven and dryer in the late afternoon. Anything that gives off heat adds to what the air conditioner must remove, at the hour it is already losing ground.
What helps instead
- Put the thermostat where you can live, somewhere in the mid to upper 70s, and leave it alone.
- Change the filter before the heat arrives rather than after the system fails, since restricted airflow is what freezes coils and overheats blowers when the system runs around the clock.
- Keep two feet clear around the outdoor unit and rinse the salt film and clippings off the coil.
- Draw the blinds and curtains on sun-facing windows through the afternoon.
- Cook on the stovetop or the grill, and save the dryer and dishwasher for after dark.
- Run ceiling fans, which do not lower the temperature but make moving air feel several degrees cooler, so the thermostat can stay higher.
Signs to act on that day
A system under strain gives notice before it quits: air at the vents that is merely cool rather than cold, indoor humidity rising while the temperature holds steady, a sound from the outdoor unit you have not heard before, short cycling or a unit that runs for hours and still loses ground, and water in the drain pan. Any of these during a heat wave is a reason to reach out that day rather than hoping the system recovers, because the parts that fail in heat do not recover on their own.
The spring visit is how this gets avoided
Every mechanical failure on this list is found during a spring maintenance visit, when the capacitor is tested under load, the coils are cleaned, the charge is checked, the connections are tightened against corrosion, and the drain is cleared. Russell’s American Mechanical has served Hampton Roads since 1977, and our maintenance visits are built around exactly those items. Members of the Premium Home Care Agreement receive two visits a year and priority scheduling when a heat wave fills the phones, and any homeowner can schedule online, through the website chat, or by phone, with same-day appointments available by phone when the day allows.