How Air Conditioning Works: The Refrigerant Cycle Explained

How Air Conditioning Works and the Refrigerant Cycle Explained

Your air conditioner does not create cold out of thin air. It moves heat. The system collects heat from the air inside your home, carries that heat outside, and rejects it to the outdoor air. The engine that makes this possible is the refrigeration cycle. The working fluid inside that cycle is the refrigerant. In most San Jose homes we service, that refrigerant is either R-22 in older systems or R-410A in modern equipment. This article explains the cycle in clear language, shows where the saturated state lives inside your equipment, and connects those ideas to practical service procedures like charging, superheat, and subcooling verification. If you want reliable comfort, low utility bills, and long equipment life, understanding these basics matters.

How the refrigeration cycle actually moves heat

Every vapor compression air conditioner has four essential parts that cooperate to move heat. The compressor pulls cool, low-pressure vapor from the indoor coil and compresses it into a hot, high-pressure vapor. The outdoor coil, called the condenser, removes heat from that vapor until it condenses into a high-pressure liquid. A metering device, such as a TXV or an orifice, then drops the pressure of that liquid. The indoor coil, called the evaporator, receives the low-pressure liquid and allows it to boil into vapor while it absorbs heat from the indoor air. The compressor then pulls that vapor in again, and the loop continues. When you stand next to the outdoor unit and feel warm air blowing up, you are feeling your home’s heat being rejected to the outdoors.

Refrigerant as the heat carrier

The refrigerant is chosen because it boils and condenses at temperatures that are useful for comfort cooling. In older residential systems, R-22 was common. It operates at moderate pressures and can provide dependable cooling when installed and serviced correctly. Due to its ozone depletion potential, it is no longer produced for new use in the United States. In most modern residential systems, R-410A is now standard. It operates at higher pressures, has no ozone depletion potential, and delivers strong heat transfer when the charge is correct and the airflow is right. Both refrigerants follow the same thermodynamic rules. Pressure and temperature move together in their saturated state. Technicians use that relationship to verify the health of the system.

The saturated state in plain language

When a refrigerant changes state, it is saturated. During boiling or condensing, large amounts of heat are absorbed or rejected while the temperature remains essentially constant for a given pressure. A helpful way to visualize this is to think of a pot of water with a lid. At a steady boil the water stays near the same temperature as long as liquid water remains in the pot, yet it continues to absorb heat. Refrigerants are engineered to boil at much lower temperatures than water, which makes them useful in air conditioning. Inside an operating AC system, saturation happens in two places. In the evaporator, the refrigerant boils and absorbs heat from the indoor air. In the condenser, the refrigerant condenses and rejects heat to the outdoor air. When the system is off and pressures are equalized, the entire refrigerant charge rests at a saturation pressure that corresponds to the system temperature.

Pressure, temperature, and why the relationship matters

In the saturated state, each refrigerant has a specific pressure for each temperature. Lowering the pressure lowers the saturation temperature and encourages boiling. Raising the pressure raises the saturation temperature and encourages condensing. Technicians use a pressure and temperature chart or digital tools to connect these values to real measurements in the field. On R-410A, for example, a common condenser saturation temperature on a warm day might be in the range that gives a head pressure near 300 pounds per square inch.

Superheat and subcooling explained

Superheat describes how many degrees the refrigerant vapor is above its saturation temperature as it leaves the evaporator. It proves that the liquid in the indoor coil has fully boiled into vapor before it returns to the compressor. Proper superheat protects the compressor from liquid floodback and shows that the indoor coil is being fed correctly for the current load and airflow.

Subcooling describes how many degrees the refrigerant liquid is below its saturation temperature as it leaves the condenser. It proves that the outdoor coil has fully condensed vapor into a solid column of liquid for delivery to the metering device. Proper subcooling provides stable capacity and prevents the metering device from being starved by flashing liquid in the liquid line.

When a technician measures pressures and line temperatures, calculates superheat and subcooling, and compares those values with the target ranges for the refrigerant in your system, that technician is confirming correct charge and healthy heat transfer. These measurements are not optional details. They are the core of accurate charging and long-term reliability.

R-22 versus R-410A in everyday service

R-22 systems are aging. The refrigerant is limited and priced accordingly. If an R-22 system is tight, uses reasonable energy, and is comfortable, repairs can still make sense. For major leaks or compressor problems, replacement often provides better long-term value because new equipment delivers higher efficiency, easier service, and readily available refrigerant. When service is performed on R-22 equipment, careful leak checks, clean evacuations, and correct airflow are essential to protect remaining life.

R-410A systems bring higher operating pressures and modern compressors. That combination demands precision. Evacuation needs to reach an appropriate micron level with a verified decay test, filter driers must be installed and replaced after burnouts, liquid line restrictions must be eliminated, and charge must be dialed in with verified subcooling or superheat based on the metering device. Airflow across the evaporator must meet the equipment’s design because refrigerant charge targets assume correct airflow. When these steps are done, R-410A systems provide quiet, efficient, and stable comfort across San Jose’s summer conditions.

Why changes of state move so much heat

It takes relatively little heat to raise the temperature of a liquid that stays a liquid. It takes far more heat to change that liquid into a vapor. The same is true when a vapor condenses back into a liquid. This property is the heart of the refrigeration cycle. During boiling in the evaporator, the refrigerant absorbs a large quantity of heat as it changes state, even though its temperature remains near the same saturation temperature. During condensing in the condenser, that same amount of heat is rejected as the refrigerant returns to liquid. This is why phase change gives us powerful heat transfer with compact coils and reasonable airflow.

What correct charging looks like in the field

Accurate charging starts long before any refrigerant is added. The system must be tight, clean, and dry. The filter must be clean. Blower settings must match the equipment size and ductwork. Coils must be free of debris and biofilm. Only then do pressure and temperature readings mean what they should. For fixed orifice systems, technicians target superheat under current load and airflow. For TXV systems, technicians set charge by subcooling and confirm that the TXV is controlling superheat properly. On both refrigerants, technicians verify that condenser saturation temperature tracks outdoor ambient by a reasonable approach and that evaporator saturation temperature sits in a band that balances comfort and efficiency.

Undercharge often shows as low suction pressure, low evaporator saturation temperature, high superheat, long run times, and icing on the indoor coil or suction line. Overcharge often shows as high head pressure, poor efficiency, elevated condenser saturation temperature, and low superheat that risks liquid refrigerant returning to the compressor. The cure is not guesswork. The cure is clean measurement and correct adjustment against targets that match the refrigerant and the metering device.

Environmental context without the jargon overload

Refrigerants have two key environmental metrics. Ozone depletion potential describes damage to the ozone layer. Global warming potential describes the relative contribution to warming. R-22 has ozone depletion potential, which is why it was phased down. R-410A has no ozone depletion potential, but it does have global warming potential. Industry research has produced new families of refrigerants with lower global warming potential, along with natural refrigerants that have no ozone impact and very low warming impact. Those options require specific safety measures and careful system engineering. For most Bay Area homes today, the practical choice is to maintain an existing R-22 system if it is healthy, or to install a modern R-410A system that is sized and charged correctly. That approach balances comfort, cost, and serviceability.

What homeowners can do to protect performance

Good maintenance multiplies the value of correct charging. Keep shrubs and fences back from the outdoor unit so the condenser can breathe. Replace or wash filters on schedule so the evaporator gets design airflow. If you notice icing, short cycling, or a sudden change in comfort, shut the system off and call for service before the compressor is damaged. During every professional visit, ask for documented pressures, temperatures, superheat, and subcooling. Those numbers create a performance baseline that makes the next check more meaningful.

Why choose Silicon Valley Comfort for charging and service

We approach every system with careful preparation and measurement. Expect clean coils, verified airflow, tight evacuation targets with a decay check, new filter driers after burnouts, and charge set by the correct method for your metering device. Expect readings recorded before and after service. Expect clear explanations that connect those numbers to comfort and energy use. Whether your system uses R-22 or R-410A, our goal is stable capacity, quiet operation, and fewer surprises during the hottest weeks of the year.

Answers to common questions

Is it worth repairing an R-22 system?

If the unit is tight, the compressor is healthy, and comfort is acceptable, targeted repairs can still be the right move. When leaks are large or compressors fail, replacement often delivers lower lifetime cost and better efficiency.

Does R-410A require special handling?

Yes. It runs higher pressures. Accurate charging, verified superheat or subcooling, correct line sizing, and careful evacuation are all required for compressor life and efficiency.

How quickly does a correct charge improve comfort?

When airflow is correct and coils are clean, a proper charge improves capacity and stability during the same visit. The full benefit shows up on the hottest afternoons when the system holds setpoint without excessive run time.