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HVAC Glossary

HVAC Glossary and Terminology

Plain-English definitions of the HVAC terms you will see in quotes, manuals, and repair estimates – from SEER2 and AFUE to heat pumps and MERV ratings.

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HVAC Glossary and Terminology

From compressors to the new Puron Advance (R-454B) refrigerant, here is a plain-English guide to the HVAC parts, ratings, and terms you will hear from your technician – plus the common problems homeowners search for.

Refrigerants

R-454B (Puron Advance)
The new low-GWP refrigerant in Bryant and Carrier 2025+ systems, replacing R-410A under the EPA phase-down. An A2L (mildly flammable) refrigerant that needs A2L-rated equipment and trained handling.
R-410A (Puron)
The previous standard AC and heat pump refrigerant, now being phased down for its high global-warming potential.
R-32
A low-GWP A2L refrigerant some manufacturers use as an R-410A replacement.
R-22 (Freon)
The old refrigerant phased out in 2020; no longer produced, so older systems are costly to service.
GWP (Global Warming Potential)
A measure of how much a refrigerant contributes to warming – the reason R-410A is being replaced.
A2L Refrigerant
The mildly-flammable, low-toxicity safety class of newer refrigerants like R-454B and R-32.
Refrigerant
The fluid that absorbs and releases heat as it cycles through your system to cool or heat your home.

Air Conditioning Parts

Compressor
The heart of your AC; it pressurizes refrigerant to move heat out of your home.
Condenser Coil
The outdoor coil that releases the heat your system pulls from inside.
Evaporator Coil
The indoor coil that absorbs heat and cools your air.
Capacitor (Run/Start)
Gives the motors the electrical push to start and keep running; a very common failure part.
Contactor
An electrical switch that powers the outdoor unit; it wears out over time.
Expansion Valve (TXV)
Meters the exact amount of refrigerant into the evaporator coil.
Condenser Fan Motor
Pulls air across the outdoor coil to release the heat removed from your home.
Filter Drier
Removes moisture and debris from the refrigerant to protect the system.
Refrigerant Lines
The copper suction and liquid lines that carry refrigerant between the indoor and outdoor units.
Service Ports (Schrader Valves)
Where a technician connects gauges to read system pressures.
Condensate Drain Line
Carries off the water your AC removes from the air; clogs cause leaks and shutoffs.
Float / Safety Switch
Shuts the system off if the condensate drain backs up, preventing water damage.
Disconnect Box
The outdoor electrical shut-off for the AC unit.
Air Handler
The indoor unit that circulates conditioned air through your ducts.

Heating & Furnace Parts

Heat Exchanger
Transfers heat to your air; a crack can leak carbon monoxide, so safety matters here.
Burner
Where gas is ignited to create heat.
Igniter (Hot Surface)
Heats up to light the burners – the modern replacement for a pilot light and a common failure part.
Flame Sensor
Confirms the burner actually lit; when dirty, the furnace shuts itself off.
Pilot Light
The small standing flame in older furnaces that ignites the burners.
Gas Valve
Controls the flow of gas to the burners.
Draft Inducer Motor
Pulls combustion gases out through the flue before the burners light.
Pressure Switch
Confirms safe venting before the furnace is allowed to fire.
Flue / Vent Pipe
Safely carries combustion gases out of your home.
Rollout Switch
A safety control that cuts the gas if flames escape the burner area.
Limit Switch
A safety control that shuts the furnace off if it overheats.
Blower Motor
Pushes heated or cooled air through your ducts.
Control Board
The furnace control that sequences ignition, blower, and safety devices.
Thermocouple
A safety device that shuts off the gas if the pilot light goes out.

Heat Pump Parts

Reversing Valve
Lets a heat pump both heat and cool by reversing the flow of refrigerant.
Defrost Cycle
Briefly reverses to melt frost off the outdoor coil in cold weather.
Auxiliary / Emergency Heat
Backup electric heat that kicks in during very cold spells.
Air-Source Heat Pump
Moves heat between your home and the outdoor air for year-round comfort.
Accumulator
Protects the compressor by keeping liquid refrigerant out of it.
Defrost Control Board
Manages the heat pump defrost cycle in cold weather.

Indoor Air Quality

MERV Rating
How well an air filter traps particles; higher catches more (check the system max).
HEPA Filter
A high-efficiency filter that captures very fine particles.
Air Scrubber
A device that actively reduces airborne contaminants, odors, and germs.
UV (Germicidal) Light
Kills mold and bacteria on the coil and in the airstream.
Whole-Home Air Purifier
Cleans the air for your entire house through the HVAC system.
Humidifier / Dehumidifier
Adds or removes moisture to keep indoor air comfortable.
Air Filter
Traps dust and particles to protect your system and improve your air.
Fresh-Air Ventilation
Brings filtered outdoor air in to reduce stale, recirculated air.

Ductwork

Plenum
The central box where conditioned air enters and leaves the duct system.
Supply & Return Ducts
Supply carries air to your rooms; return pulls it back to the system.
Duct Sealing
Closing leaks so you are not paying to heat and cool your attic.
Static Pressure
The blood pressure of your duct system; too high strains the blower.
Damper
An adjustable plate that controls airflow to different rooms or zones.
Register / Vent
The grille where conditioned air enters a room.

Ratings & Efficiency

SEER2
An AC cooling-efficiency rating; higher means lower energy bills.
EER
Energy Efficiency Ratio – how efficiently a system cools on the hottest days at peak temperature.
AFUE
Furnace efficiency rating – the percentage of fuel turned into usable heat.
HSPF2
A heat pump heating-efficiency rating; higher means lower bills.
BTU
British Thermal Unit – a measure of heating or cooling energy.
Ton
A measure of cooling capacity; one ton equals 12,000 BTU per hour.
Load Calculation (Manual J)
The proper method for sizing a new system to your home.
Variable-Speed / Two-Stage
Systems that adjust output for steadier comfort and lower bills versus single-stage on/off.
Superheat & Subcooling
Readings a technician uses to confirm your system has the correct refrigerant charge.
Zoning
Using dampers and multiple thermostats to control temperature room-by-room.
Thermostat
The control that tells your system when to heat or cool; smart models learn your schedule.

Common Problems People Search

AC Blowing Warm Air
Often low refrigerant, a failed capacitor or compressor, or a dirty coil.
Frozen Evaporator Coil
Ice on the indoor coil, usually from low airflow or low refrigerant.
Short Cycling
When the system rapidly turns on and off; signals a sizing, thermostat, or electrical issue.
No Heat / Furnace Will Not Start
Often a bad igniter, flame sensor, or gas-supply problem.
Furnace Blowing Cold Air
Could be a thermostat setting, a failed igniter, or an overheating shutdown.
Loud HVAC Noises
Banging, squealing, or rattling that usually points to a loose, worn, or failing part.
Water Leaking From the Unit
Most often a clogged condensate drain or a frozen coil that has thawed.
Bad Smell From Vents
Can signal mold in the system, a dirty filter, or an electrical issue.
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5-star rated

What your neighbors say

Real reviews from real Orange County homeowners.
★★★★★

I cannot thank South County Air Services enough for impeccable customer service. Behshad came out on a Saturday to check my heating unit (failing motor). He was professional, knowledgeable, courteous and thorough – extremely fair pricing, with open and honest communication. Highly recommend. Five star plus!

KM

Kelly M.
Verified Yelp review
★★★★★

Super impressed with our experience. We needed to replace our 40+ year old furnace, and from the first call everything was easy and clearly explained. Responsive, great follow-up, great pricing, timely booking, installers on time and prepared, clean install, no mess left.

DM

D. M.
Verified Yelp review
★★★★★

I am grateful to the technician who inspected my HVAC system today. I feel he did a thorough inspection and told me the truth about my unit. I had two other companies beforehand – the first gave me a report that would call for major expenditure.

EM

Elena M.
Verified Yelp review
★★★★★

You will not find a more honest and knowledgeable HVAC tech. They show up on time and are very professional, but most of all will not try to upcharge you. He could have charged me significantly more but cares about diagnosing the actual problem. I found my HVAC tech – 10 star review if I could!

PV

Pat V.
Verified Yelp review
★★★★★

It’s not often you find an honest business willing to give suggestions over the phone to troubleshoot why my HVAC wasn’t working – without charging me. After a couple minutes we determined my breaker popped and all I needed was to reset it. I appreciate Behshad and will definitely use him in the future.

HJ

Heng J.
Verified Yelp review
★★★★★

I spoke with the owner on a Saturday morning and he was at my house within 45 minutes. Another company wanted $3,000 in repairs; Behshad recommended a simple $250 repair that fixed the issue. Very honest, thorough, and reliable!

AS

Alex S.
Verified Google review
★★★★★

I cannot thank South County Air Services enough for impeccable customer service. Behshad came out on a Saturday to check my heating unit (failing motor). He was professional, knowledgeable, courteous and thorough – extremely fair pricing, with open and honest communication. Highly recommend. Five star plus!

KM

Kelly M.
Verified Yelp review
★★★★★

Super impressed with our experience. We needed to replace our 40+ year old furnace, and from the first call everything was easy and clearly explained. Responsive, great follow-up, great pricing, timely booking, installers on time and prepared, clean install, no mess left.

DM

D. M.
Verified Yelp review
★★★★★

I am grateful to the technician who inspected my HVAC system today. I feel he did a thorough inspection and told me the truth about my unit. I had two other companies beforehand – the first gave me a report that would call for major expenditure.

EM

Elena M.
Verified Yelp review
★★★★★

You will not find a more honest and knowledgeable HVAC tech. They show up on time and are very professional, but most of all will not try to upcharge you. He could have charged me significantly more but cares about diagnosing the actual problem. I found my HVAC tech – 10 star review if I could!

PV

Pat V.
Verified Yelp review
★★★★★

It’s not often you find an honest business willing to give suggestions over the phone to troubleshoot why my HVAC wasn’t working – without charging me. After a couple minutes we determined my breaker popped and all I needed was to reset it. I appreciate Behshad and will definitely use him in the future.

HJ

Heng J.
Verified Yelp review
★★★★★

I spoke with the owner on a Saturday morning and he was at my house within 45 minutes. Another company wanted $3,000 in repairs; Behshad recommended a simple $250 repair that fixed the issue. Very honest, thorough, and reliable!

AS

Alex S.
Verified Google review

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HVAC in Terminology: what local homeowners should know

Terminology homeowners deal with the same Orange County reality: hot inland summers, aging systems in older neighborhoods, and HOA or permit rules that change from community to community. As a local, owner-operated shop based in nearby Tustin, we size every system to the home, fix what is actually wrong, and quote flat-rate pricing before we start — never a commissioned upsell.

South County Air Services is a family-owned, owner-operated HVAC company based in Tustin, CA (CSLB license #1062690), holding a 5.0-star Google rating across 205+ reviews. We serve all of Orange County 24/7 with flat-rate pricing, and as a Bryant dealer we install, repair, and maintain air conditioning, heating, heat pump, and indoor-air-quality systems. Because the licensed owner runs the jobs — not a commissioned salesperson — our customers consistently say we give honest recommendations and do not upsell.

What Terminology-area customers say

★★★★★

“A wonderful experience with Behshad and his team. They came out quickly, arrived on time, and fixed our HVAC issues with ease. They will be our first call in the future.”

— Chris Connell, Google review
★★★★★

“Behshad was so friendly and efficient. He showed up within an hour and a half of my call, looked at my system, and showed me I was not using the thermostat correctly. Wonderful service.”

— Shelly Houck, Google review
★★★★★

“A client’s property had a carbon monoxide detector going off — we found a gas leak at the heater. I called in the morning and they were there with a new heater by 3 PM that day. Professional, friendly, and efficient.”

— Dianna McGarvin, Google review

Read all 228 five-star Google reviews →

Common questions from Terminology homeowners

How much does AC repair cost in Terminology?

Most AC repairs in Terminology run about $150–$600 depending on the part — a failed capacitor is roughly $150–$300 and a refrigerant recharge $300–$600, plus a diagnostic fee. We quote a flat rate before any work starts, so there are no hourly surprises.

How much does it cost to replace an AC or HVAC system in Terminology?

A like-for-like AC or furnace replacement in Terminology typically runs $8,000–$14,000, and higher-efficiency or full heat-pump systems $14,000–$21,000+, depending on size, SEER2 efficiency, ductwork, and permit or HOA factors. You get a written flat-rate quote, and we never upsell equipment you do not need.

Do I need a permit to replace my AC or furnace in Terminology?

Yes. California requires a permit for any AC or furnace replacement in Terminology — even a like-for-like swap — plus a HERS test (duct-leakage and refrigerant verification). As your licensed contractor (CSLB #1062690) we pull the permit and handle the inspection, so the work is code-compliant and documented for resale.

How long does an AC system last in Terminology?

With regular maintenance, most AC systems in Terminology last about 12–15 years, and up to about 20 with good care. Terminology’s inland summer heat means longer run times, so skipping maintenance shortens that noticeably.

Why is my AC not blowing cold air?

The most common causes are low refrigerant from a slow leak, a failed capacitor, a frozen evaporator coil, or a clogged air filter. It is usually a repair, not a replacement — we diagnose the actual cause and show you the failed part before quoting.

How often should I change my HVAC filter?

Every 60–90 days for a standard 1-inch filter, or monthly during heavy summer use or with pets. It is the cheapest thing you can do to protect the system and keep energy bills down.

Do you offer same-day or emergency HVAC repair in Terminology?

Yes — same-day and 24/7 emergency AC and furnace repair across Terminology and south Orange County. Call (949) 933-3130 and we will get a technician out fast with a flat-rate price before any work begins.

Who is the best HVAC company in Terminology?

We will let the reviews speak — South County Air Services holds a 5.0-star rating across 200+ reviews. Family-owned, owner-operated, licensed (CSLB #1062690), a Bryant dealer, with flat-rate pricing and no upsells.

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