HVAC, explained
How an Air Conditioner Works
An air conditioner does not make cold air. It moves heat out of your house using a refrigerant that absorbs heat indoors, carries it outside, and releases it there before returning to start again. Cooling the air is only half the job; the same process pulls moisture out of it, which is why runtime matters as much as capacity in Florida.
Most explanations of air conditioning start with a diagram and four part names, which tells you what the pieces are called without telling you what is actually happening. The useful idea is simpler: your air conditioner is a heat-moving machine, not a cold-making one. Once that clicks, almost everything else about how the system behaves, including why it struggles on the most humid days, follows from it.
An air conditioner moves heat, it does not create cold
There is no such thing as a cold generator. Cold is simply the absence of heat, so the only way to cool a room is to take the heat that is in it and put that heat somewhere else. Your air conditioner is a pump for heat. It picks heat up inside your house and sets it down outdoors, over and over, for as long as it runs. That is the entire purpose of the equipment, and every component in it exists to serve that one errand. This is why your outdoor unit blows hot air. People sometimes assume that hot exhaust means something is wrong or wasteful, but it is the proof the system is working: the heat coming off that outdoor coil is the heat that used to be in your living room. It is also why an air conditioner cannot cool a space with its outdoor unit sitting in the same room. The heat has to have somewhere else to go, and if it has nowhere to go, you have a very expensive fan. The same principle explains a heat pump, which is an air conditioner that can run its cycle in both directions. In summer it moves heat from inside to outside. In winter it reverses and moves heat from the outdoor air into your house, which sounds impossible until you remember that even cold air contains heat. Nothing about the machine changes; only the direction of the errand does, which is the heart of how a heat pump compares with a furnace. Understanding air conditioning as heat transport rather than cold production is what makes the rest of this page predictable instead of something to memorize.
The refrigeration cycle, in the order it actually happens
The heat gets carried by a working fluid called refrigerant, chosen because it boils and condenses at temperatures useful for this job. The cycle has four stages and they always run in the same order. First, in the evaporator coil, which sits indoors in the airflow of your blower, low-pressure liquid refrigerant absorbs heat from your house air and boils into a vapor. Your warm indoor air passes over that cold coil, gives up its heat, and continues into the ducts noticeably cooler. Second, that vapor reaches the compressor, usually in the outdoor unit, which squeezes it to a much higher pressure. Compressing a gas raises its temperature, and this step is deliberate: the refrigerant has to end up hotter than the outdoor air, because heat only flows from hotter to colder on its own. The compressor is the single largest electricity user in the system, which is why compressor health drives both your power bill and your repair bills. Third, the hot high-pressure vapor flows through the condenser coil in the outdoor unit, where a fan pushes outside air across it. The refrigerant is hotter than that air, so it sheds its heat into it and condenses back into a liquid. This is the moment the heat from your house finally leaves your property. Fourth, the still-pressurized liquid passes through an expansion device, a metering valve or orifice that drops its pressure sharply. Pressure and temperature fall together, so the refrigerant emerges cold enough to absorb heat again, and it arrives back at the evaporator ready to repeat the loop. Four stages, one continuous circuit, running as long as the thermostat is calling.
The second job: pulling water out of the air
Cooling is the half of the job everyone knows about. Dehumidifying is the half that decides whether a Florida house actually feels comfortable, and it happens as a direct consequence of the same cycle. The evaporator coil runs colder than the dew point of the air moving across it, so water vapor, which is the moisture carried invisibly in air, condenses on the coil the same way it beads on a glass of iced tea. That water collects in a drain pan and leaves through the condensate line. On a humid day a residential system can remove a surprising volume of water this way, and none of it is incidental to comfort: air at the same temperature feels markedly cooler and less oppressive when its moisture has been taken down. The critical detail is that this takes time. Moisture removal depends on sustained runtime, because the coil has to stay wet and cold long enough to keep condensing water out of the air passing over it. A system that cools the house in short, fast bursts satisfies the thermostat and shuts down before much water has come off the coil. The thermometer reads correctly and the house still feels clammy. This is the mechanism behind one of the most common and most expensive mistakes in residential HVAC, which is installing more capacity than the house needs. An oversized unit is extremely good at the job you can measure and poor at the job you can feel. In a hot-humid climate that trade is a bad one, which is why sizing is done with a load calculation rather than a rule of thumb, and why what BTU actually measures matters more than the biggest number on the box, and why a system that seems to be cooling fine can still leave a home uncomfortable.
What the parts look like in a real house
In most Florida homes the equipment is a split system, meaning it is split into an indoor half and an outdoor half connected by refrigerant lines. The indoor half is the air handler, often in a garage, closet or attic. It contains the blower that moves air through your ducts, the evaporator coil the air passes over, the filter, and the drain pan under the coil. The outdoor half is the unit on the pad beside your house, containing the compressor, the condenser coil, and the fan that pulls outdoor air through that coil. Two insulated copper lines run between them, one carrying cold low-pressure refrigerant in and one carrying hot high-pressure refrigerant out. Knowing which box holds what makes symptoms much easier to interpret. Water around the indoor unit points to the drain pan and condensate line, not to the outdoor equipment, which is the usual story behind an air conditioner leaking water. An outdoor unit running while indoor airflow has stopped points at the blower. Ice on the indoor coil usually points to restricted airflow or low refrigerant charge, the same pair behind most cases of an AC that runs but will not blow cold, both of which keep the coil colder than it should be. A ductless mini-split uses the same four-stage cycle with the indoor coil mounted directly on a wall in the room it serves, which is why it needs no ductwork. A packaged or rooftop unit puts every component in one cabinet outside, common on commercial buildings and some manufactured homes. The arrangement differs; the physics does not.
Efficiency, and what Florida actually requires
Two air conditioners can move the same amount of heat while using very different amounts of electricity, which is what efficiency ratings describe. The current measure for central systems is SEER2, the seasonal energy efficiency ratio: total heat removed across a cooling season divided by the electrical energy consumed over that same season. A higher SEER2 means less electricity for the same cooling. There is also the energy efficiency ratio 2 (EER2), which measures efficiency at a single hard-working moment rather than across a season, and matters most in climates where the system spends long stretches at peak load. The federal minimums are regional, and Florida's region is the one that matters here. The Department of Energy divides the country into North, Southeast and Southwest, and places Florida in the hot-humid Southeast. For split-system air conditioners installed on or after January 1, 2023, the Southeast minimum is 14.3 SEER2 for units with cooling capacity under 45,000 Btu per hour, and 13.8 SEER2 at or above that capacity. The Northern minimum is lower, at 13.4 SEER2, so a number quoted from a national article may not be a legal installation in Florida. One caution when comparing equipment: SEER2 and the older SEER scale are measured differently and are not directly comparable, so a SEER2 figure cannot be read against a SEER figure from an older unit as though they were the same scale. Compliance is determined by a model's measured SEER2. ENERGY STAR certification sets a bar above the federal floor for equipment that qualifies.
Frequently asked
Does my air conditioner bring in fresh air from outside?
Generally no. A standard residential air conditioner recirculates the air already inside your house, cooling and dehumidifying it on each pass. The outdoor unit exchanges heat with outside air, but that air does not enter your ductwork. Fresh air comes in through a separate ventilation path, if your house has one, or through ordinary leakage. This is why running the air conditioner does not clear indoor odors or stuffiness on its own.
Why would my AC run constantly and still not cool the house?
Because the system can be running while the heat-moving cycle is impaired. Common causes include a clogged filter or blocked return starving the coil of airflow, a dirty outdoor condenser coil that cannot shed heat into the outside air, low refrigerant charge from a leak, or a failing compressor. Capacity that is simply too small for the house produces the same symptom on the hottest days. The pattern is worth noting too: short bursts suggest something different from one long run that never satisfies.
Does closing vents in unused rooms save money?
Usually not, and it can cost you. Your blower is designed to move a certain volume of air against a certain resistance. Closing vents raises that resistance, which reduces total airflow across the evaporator coil and can push the coil colder than intended. Reduced airflow works against both cooling and moisture removal, and in some systems it raises duct leakage. Rooms you are not using are better handled by a system designed for zoning than by shutting registers.
Is a higher SEER2 number always worth paying for?
Not automatically. A higher SEER2 does mean less electricity for the same cooling, so the savings are real, but how quickly they repay the extra cost depends on how many hours the system runs, what you pay per kilowatt-hour, and how well the house holds the conditioned air. In a hot-humid climate with long cooling seasons the case is stronger than in a mild one. Insulation, air sealing, duct condition and correct sizing often move comfort and bills more than the rating on the box does.
Do I need to call a pro for this?
No. Understanding how your system works takes nothing but reading, and the checks worth doing yourself are genuinely simple: look at the air filter and change it if it is dirty, confirm the thermostat is set to cool and to a temperature below the room, and clear leaves, grass clippings and stored items away from the outdoor unit and from your indoor returns and vents. Those three things resolve a real share of no-cooling calls at no cost. Past that point the work is not homeowner work. Anything involving refrigerant, the compressor, wiring, a capacitor or a sealed system belongs to a licensed contractor, because refrigerant is handled under federal rules and the outdoor unit holds stored electrical charge even with the breaker off.
Related
Blume Mechanical Service is a licensed commercial and residential HVAC contractor serving Florida's Tampa Bay region (CAC-1822618). If your system is running but the house is not comfortable, that is a diagnosis, not a guess.
Sources: US Department of Energy — 2023 central air conditioner standards, regional SEER2 minimums · US Department of Energy — guide to home heating and cooling · US Department of Energy — HVAC guide for contractors to share with homeowners · ENERGY STAR — central air conditioner and heat pump specification