Terms Nobody Bothers
to Explain

The indoor part of your split AC system — the cabinet in your attic, closet, or utility room that contains the evaporator coil, blower fan, and filter. It moves air across the cold coil and distributes it through your ductwork. In a heat pump system, the air handler also contains the electric resistance backup heat strip. Often confused with the furnace, which it replaces in Florida's all-electric split systems.

Measured in cubic feet per minute. A properly sized Florida system delivers roughly 400 CFM per ton of capacity. Too little airflow (from a dirty coil, undersized ducts, or clogged filter) reduces both cooling and dehumidification. Too much airflow reduces latent capacity — the air moves too fast across the coil to have moisture removed effectively.

Air Conditioning, Heating, and Refrigeration Institute. The industry body that certifies matched system efficiency ratings. When a contractor specifies a "matched system," the AHRI rating is the tested efficiency of that specific outdoor unit + air handler combination — not the efficiency of either unit alone. Always verify AHRI certification on a proposed system.

The basic unit of heat energy in HVAC. One BTU is the energy needed to raise one pound of water by one degree Fahrenheit — roughly the heat from one burning match. AC systems are rated in BTU per hour. 12,000 BTU/hr = 1 ton of cooling. A 3-ton system moves 36,000 BTU of heat per hour from inside your home to outside.

The fan motor inside the air handler that moves air through the system. PSC motors (permanent split capacitor) run at fixed speeds and are found in older and budget systems. ECM motors (electronically commutated motor) are variable speed, dramatically more efficient, and far better for Florida humidity control because they can run at low speed for extended periods — maximizing moisture removal.

A small cylindrical electrical component that stores and releases energy to start and run the compressor and fan motors. Florida heat degrades capacitors faster than anywhere else — they're one of the most common AC failure points in this climate. A weak capacitor causes hard starts, reduces efficiency, and eventually kills the compressor. We test capacitor microfarads on every maintenance visit. Replacing a $35 capacitor proactively is a very different conversation than replacing a $2,000 compressor reactively.

Two coils work together in a split system. The evaporator coil is indoors — refrigerant inside it absorbs heat and moisture from your home's air. The condenser coil is in the outdoor unit — it releases that heat to the outside air. Both are made of copper tubing and aluminum fins, though some manufacturers now use all-aluminum coils. Dirty coils are the leading cause of efficiency loss and comfort problems.

The heart of the refrigeration system — a pump that compresses refrigerant gas and drives it around the refrigerant circuit. It lives in the outdoor unit. The most expensive component to replace ($1,500–$3,000 for the part alone). Most compressor failures are caused by preventable conditions: low refrigerant, weak capacitors, dirty coils, or low airflow. A well-maintained Florida compressor should last 15+ years.

The water that drips off your evaporator coil is condensate — moisture removed from your home's air. It collects in the drain pan and exits through the condensate drain line (typically a PVC pipe). In Florida, a 3-ton system removes 20–30 pints of water per day in summer. That drain line clogs with algae and biofilm regularly. A clogged drain line is the #1 cause of AC-related water damage in Florida homes.

An electrical switch in the outdoor unit that connects line voltage to the compressor and condenser fan motor when the thermostat calls for cooling. Contactors wear out — the contact points burn and pit over time, causing slow engagement, voltage drop, and eventually failure. Like capacitors, they're inexpensive to replace proactively and expensive to ignore.

The temperature difference between the air entering the return and the air leaving the supply register. A properly operating Florida system should show 14–22°F delta-T across the air handler under normal conditions. Too low means insufficient cooling or low airflow. Too high may indicate low refrigerant or restricted airflow. Delta-T is one of the first numbers we check on a service call.

The temperature at which air becomes saturated and water starts to condense. In Clearwater in July, the outdoor dew point is typically 72–76°F — meaning any surface cooler than 72°F will collect condensation. This is why your supply registers sweat, why pipes drip, and why your AC coil drains so much water. Dew point is a more reliable comfort indicator than relative humidity — a dew point above 65°F feels uncomfortable regardless of temperature.

The network of channels that distribute conditioned air through your home. Supply ducts carry cool air from the air handler to each room. Return ducts bring room air back to the air handler. Florida homes use a mix of sheet metal trunk lines and flexible duct runs. Flex duct in attics is particularly vulnerable to disconnection, compression, and moisture absorption. Duct leakage in Florida attics running at 140°F is a major efficiency loss.

A measure of cooling efficiency at a fixed outdoor temperature (95°F). Unlike SEER (which averages across a range of temperatures), EER tells you how efficiently a system performs at peak Florida conditions. For Florida homeowners, EER is actually more relevant than SEER — your system spends most of its time at or near peak load conditions, not the average conditions SEER is calculated from.

A variable-speed blower motor that adjusts airflow continuously rather than running at fixed speeds. Uses up to 75% less electricity than a PSC motor at low speeds. The extended low-speed operation is critical for Florida humidity control — longer run times mean more moisture removed per cooling cycle. See also: Blower Motor.

A specific type of copper coil failure caused by the reaction of formic or acetic acid with copper in the presence of moisture and oxygen. Creates distinctive winding tunnels through the copper tubing that eventually cause refrigerant leaks. Common in Florida due to VOCs from building materials, cleaning products, and organic matter in the air. All-aluminum coils are immune. Formicary corrosion is why some manufacturers have moved away from copper evaporator coils entirely.

"Freon" is a brand name (DuPont/Chemours) that became generic — like Kleenex. The actual refrigerants: R-22 (phased out, now very expensive to service), R-410A (current standard, being phased out for new equipment after 2025), R-454B (the replacement, lower global warming potential). Refrigerant does not "run out" in a healthy system — if your system is low, it has a leak that needs to be found and fixed, not just topped off.

A system that moves heat rather than generating it — in cooling mode it works exactly like a standard AC; in heating mode it reverses the refrigerant flow and extracts heat from outside air to warm your home. Florida is ideal for heat pumps — our winters rarely get cold enough to challenge them, and they're 2–3x more efficient than electric resistance heat. If your system says "emergency heat" on the thermostat, you have a heat pump.

Relative humidity is the percentage of maximum moisture the air could hold at its current temperature. Target for Florida homes: 50–60% RH indoors. Above 60%, mold growth rates accelerate. The tricky part: when your AC cools the air, the same amount of water vapor represents a higher relative humidity — until the coil removes it. This is why a short-cycling oversized system often leaves a home feeling clammy even when it's cool.

The portion of an AC system's capacity dedicated to removing moisture from the air (as opposed to sensible heat — lowering air temperature). In Florida, latent capacity is often more important than sensible capacity. A properly sized system running in Florida should dedicate roughly 30–40% of its total capacity to latent load. An oversized system short-cycles before it can accomplish meaningful dehumidification.

The pair of copper refrigerant lines connecting the outdoor unit to the indoor air handler — a larger insulated suction line and a smaller liquid line. In Florida, properly insulated line sets are critical: sweating or ice on the suction line indicates an insulation or refrigerant problem. Line sets running through hot attics lose efficiency and can be damaged by heat over time.

The ACCA (Air Conditioning Contractors of America) standard calculation method for determining the correct size of an HVAC system for a specific home. It accounts for square footage, ceiling height, insulation, windows, orientation, local climate data, and occupancy. The only correct way to size a system. Many contractors "size" systems by rule of thumb (square footage ÷ 500 = tons). That's not Manual J, it's guessing — and it's why Florida homes are chronically oversized.

The scale (1–16 for residential) that rates how effectively a filter captures particles of different sizes. Florida sweet spot: MERV 8–11. Lower doesn't protect your coil or your air. Higher (MERV 13+) can restrict airflow enough to cause coil icing and reduced dehumidification in a residential system not designed for the extra resistance. See our full IAQ & Filtration guide.

The amount and type of refrigerant in your system. A correctly charged system is critical for efficiency and equipment life. Verified by measuring superheat (on TXV systems) or subcooling (on fixed orifice systems) — not by guessing from a pressure gauge. A "charge" that's low by 10% costs you 20% efficiency and reduces latent capacity significantly. Refrigerant doesn't deplete on its own — a low charge means a leak.

The efficiency rating for air conditioners — higher is more efficient. SEER is calculated by dividing total cooling output by total electrical energy input across a theoretical cooling season. SEER2 (required on new equipment after January 2023) uses a more realistic external static pressure in the test — SEER2 ratings run about 5% lower than SEER for the same equipment. Florida minimum: 15 SEER2 (14.3 SEER equivalent). Going from 14 to 18 SEER saves roughly 20% on cooling costs — meaningful in Florida where cooling runs 9 months a year.

The portion of cooling that lowers air temperature (as opposed to latent heat, which removes moisture). Your thermostat measures sensible conditions only — it has no idea what the humidity is. In Florida, sensible and latent capacity must both be considered when sizing a system. A system with great sensible capacity but poor latent capacity will hit your temperature setpoint while leaving the house feeling muggy.

The resistance the blower motor works against to push air through the duct system — measured in inches of water column (in. w.c.). Design target for most residential systems: 0.5 in. w.c. total external static pressure. Common causes of high static: dirty coil, dirty filter, undersized return duct, crushed flex duct, closed registers. High static stresses the blower motor and reduces airflow, hurting both cooling and dehumidification.

The number of degrees the liquid refrigerant has been cooled below its condensing temperature. Used to verify correct refrigerant charge on systems with a TXV metering device. Proper subcooling varies by system but typically runs 10–15°F. Too low = undercharged or restricted. Too high = overcharged. This is the measurement that tells us your refrigerant charge is right — not a pressure gauge reading alone.

The number of degrees the refrigerant vapor has been heated above its boiling point at the suction line. Used to verify correct refrigerant charge on systems with a fixed metering device (piston). Target varies by indoor wet bulb and outdoor dry bulb temperature — typically 8–28°F depending on conditions. Measuring superheat correctly requires knowing the actual ambient conditions, not just the pressures.

The control that tells your system when to run. Important Florida note: your thermostat measures temperature only — not humidity. A home at 75°F and 70% RH feels uncomfortable, but the thermostat is satisfied. This is one reason why Florida homes benefit from humidity-sensing thermostats or dedicated dehumidifiers that run independently of the cooling cycle.

The standard unit of AC capacity. 1 ton = 12,000 BTU/hr — originally the amount of heat absorbed by melting one ton of ice in 24 hours. Florida residential systems typically range from 1.5 to 5 tons. The correct size for your home requires a Manual J calculation — not square footage divided by 500. See our History of Air Conditioning for the full origin story.

A refrigerant metering device that modulates refrigerant flow into the evaporator coil based on actual suction line conditions — more precise than a fixed piston orifice. Systems with a TXV are more tolerant of refrigerant charge variation and perform better across a wider range of conditions. When your invoice says "metering device replacement," this is what it usually means. Required by most manufacturers on matched systems above a certain efficiency rating.

Describes how many operating levels a compressor has. Single-stage: 100% or off. Two-stage: 100% or ~65%. Variable speed: continuously modulates from ~25% to 100%. In Florida, variable speed is worth the premium — it runs long, slow cycles that maximize moisture removal, maintains more consistent temperature, and uses significantly less electricity at partial load. Single-stage systems cool fast, shut off fast, and leave humidity behind.