Refrigeration glossary:
the trade terms in brief.

The refrigeration circuit

A refrigeration system moves heat out of a cold room by letting a refrigerant evaporate and condense again in a closed circuit. These are the parts, and the pressures and temperatures a technician talks about.

Refrigeration cycle

The closed circuit the refrigerant flows around: compressor, condenser, expansion valve and evaporator. In the evaporator the refrigerant takes up heat from the cold room, and in the condenser it gives that heat off outside. Every part of the circuit can be measured, and drift in pressure, temperature and current shows where a fault is coming.

Compressor

The pump of the system and the part that uses the most electricity. The compressor draws refrigerant vapour from the evaporator and raises it to a higher pressure and temperature, so the heat can be given off in the condenser. Wear and faults can often be seen in its current draw weeks before it stops. Read about refrigeration breakdowns.

Condenser

The heat exchanger where the hot refrigerant vapour from the compressor gives off heat to the outdoor air or to water and turns into liquid. A dirty condenser or a failed fan raises the pressure and the power use, and in the end trips a high-pressure alarm.

Evaporator

The heat exchanger inside the cold room or display fridge. The refrigerant evaporates here at low pressure and takes up heat from the air the fans blow through the fins. Ice on the evaporator reduces its capacity, which is why it has to be defrosted at regular intervals.

Expansion valve

The valve that lets liquid refrigerant from the high-pressure side into the evaporator and drops its pressure. It meters the flow by the superheat, so the evaporator is fed the right amount. It can be thermostatic (mechanical) or electronic, and a valve that sticks or is set wrongly gives too much or too little superheat.

Liquid receiver

A vessel after the condenser where liquid refrigerant collects. The receiver evens out the fact that the system needs different amounts of refrigerant in circulation depending on the load and the season. Many small systems don’t have one.

Filter drier

A filter in the liquid line that catches moisture, acid and dirt in the refrigerant. Moisture in the circuit can freeze in the expansion valve and break down the compressor oil. A blocked filter drier causes a pressure drop and often shows as a cold or sweating filter.

Sight glass

A small window in the liquid line where the technician can see the refrigerant. Bubbles can mean the system is short of refrigerant, and many sight glasses have an indicator that changes colour with moisture. It is a quick check and no substitute for measuring pressure and temperature.

Suction pressure

The pressure on the low side, between the evaporator and the compressor. It sets the temperature at which the refrigerant evaporates. If it falls over time, the cause can be a refrigerant shortage, an iced evaporator or an expansion valve that doesn’t open enough.

Condensing pressure

The pressure on the high side, where the refrigerant condenses, also called head pressure. It rises with the outdoor temperature and with a dirty condenser or a failed fan. High condensing pressure costs electricity and wears the compressor, and if it gets too high, the high-pressure switch stops the system.

Superheat

How many degrees the refrigerant vapour has warmed up after it has evaporated, measured in kelvin at the evaporator outlet. Superheat shows whether the evaporator is fed correctly. Too little can send liquid to the compressor, too much means part of the evaporator isn’t cooling. On many systems with a thermostatic expansion valve it is typically 4 to 8 K.

Subcooling

How many degrees the liquid refrigerant has been cooled below the condensing temperature, measured in kelvin after the condenser. Subcooling makes sure only liquid, with no vapour, reaches the expansion valve. Low subcooling can point to too little refrigerant, high subcooling to too much.

Condensing unit

One unit holding the compressor, condenser and fan, usually outdoors, serving one cold room or a few display fridges. It is the most common set-up in restaurants and small shops.

Compressor rack

Several compressors on a shared frame, serving many display fridges and cold rooms at once, typically in supermarkets. Compressors switch in and out as the load changes. If the whole rack stops, every cooled space goes down together, which is why it is worth watching closely.

Refrigerants and F-gas

The refrigerant is the substance that carries the heat. Many refrigerants are powerful greenhouse gases, which is why the EU regulates them. The detailed rules are in Regulation (EU) 2024/573, and your refrigeration company has the final word on your systems.

Refrigerant

The substance that circulates in the refrigeration circuit, taking up heat when it evaporates and giving it off when it condenses. The choice of refrigerant decides the system’s pressures, efficiency, safety requirements and climate footprint. Read about refrigerants today.

Natural refrigerant

Refrigerants found in nature, such as CO2 (R744), propane (R290) and ammonia (R717). They have a very low GWP and fall outside the F-gas leak check rules. They bring their own demands instead: CO2 runs at high pressure, propane is flammable and ammonia is toxic.

HFC

Hydrofluorocarbons, the fluorinated refrigerants most used in refrigeration since the 1990s, such as R404A and R134a. They don’t harm the ozone layer, and many of them have a high GWP. The EU is cutting the amount of HFCs on the market step by step under the F-gas regulation.

HFO

Hydrofluoroolefins, a newer group of fluorinated refrigerants with a very low GWP, such as R1234yf and R1234ze. They are used on their own or blended with HFCs, as in R449A. Many HFOs and HFO blends are mildly flammable.

F-gas

The collective term for fluorinated greenhouse gases, including HFC refrigerants. Systems that contain F-gas are subject to leak checks, record keeping and certified technicians. See F-gas and leak checks.

F-gas regulation

The EU’s Regulation (EU) 2024/573 on fluorinated greenhouse gases, which replaced Regulation (EU) No 517/2014. Among other things it sets the rules for leak checks, records, certification and bans on certain refrigerants in new equipment, and it phases HFCs down towards zero by 2050. Read about the F-gas regulation.

GWP

Global warming potential: how much one kilo of a gas adds to the greenhouse effect compared with one kilo of CO2 over 100 years. CO2 has a GWP of 1, and R404A about 3,922 on the values the F-gas regulation uses. The higher the GWP, the stricter the leak checks and the faster the phase-out.

CO2 equivalent

The refrigerant charge expressed in tonnes of CO2: kilos of refrigerant times the GWP, divided by 1,000. A system with 10 kg of R404A equals about 39 tonnes of CO2 equivalent. The CO2 equivalent decides how often the system needs a leak check. Work it out for your systems on the refrigerant page.

R404A

An HFC blend that was the standard in commercial chilled and frozen storage for many years. R404A has a very high GWP of about 3,922 and is heavily restricted under the F-gas regulation. Many older systems still run on it and should have a plan for a change of refrigerant or system.

R449A

A blend of HFCs and HFOs used to replace R404A in existing and new systems. R449A has a GWP of about 1,397, around a third of R404A. When converting a system, the technician has to review the expansion valve and the oil, among other things.

R134a

A single-component HFC refrigerant with a GWP of about 1,430, used in display fridges, chillers and many small cold rooms. R134a works at lower pressures than R404A. It is also covered by the HFC phase-down.

R290 (propane)

Propane used as a refrigerant, with a GWP of about 3. R290 is very efficient and is used mainly in plug-in display fridges and small systems. It is flammable, so the charge per circuit is limited and the technician has to follow specific safety rules.

R744 (CO2)

Carbon dioxide used as a refrigerant, with a GWP of 1. R744 is now widely used in supermarkets and larger systems across northern Europe. CO2 works at very high pressures and often runs transcritical, which places demands on the components and on the technician’s training.

Transcritical CO2

A CO2 system runs transcritical when the pressure on the high side is above the critical point of CO2, at about 31 °C and 74 bar. The CO2 then doesn’t condense, and the condenser is called a gas cooler. It typically happens when it is warm outside and needs specific control to keep the system efficient.

Leak check

The legally required check of whether a system containing F-gas is tight. How often depends on the CO2 equivalent: from 5 tonnes at least every 12 months, from 50 tonnes every 6 months and from 500 tonnes every 3 months, and with a leak detection system the interval doubles. A certified technician does it and records it in the F-gas log.

Leak detection system

A permanently installed system that detects leaks and raises an alarm, usually a gas sensor in the plant room or cold room. Under the F-gas regulation it is required on systems from 500 tonnes CO2 equivalent. Maci Intelligence is a monitoring system that can see signs of refrigerant loss in pressure and temperature, read about refrigerant.

F-gas log

The records the owner of an F-gas system must keep: refrigerant type and amount, top-ups and recovery, leak checks and who did the work. The records must be kept for at least 5 years. With Maci Service Premium the log is kept digitally, see the F-gas log.

Equipment, operation and faults

The words used for cooled spaces, for how a system is controlled, and for the faults and alarms that end in a call to the technician.

Cold room

An insulated walk-in room for chilled goods, typically kept at 0 to 5 °C. It is cooled by an evaporator under the ceiling and a condensing unit or compressor rack. See refrigeration monitoring.

Freezer room

A cold room for frozen goods, typically at −18 to −25 °C, also called a cold store. Its evaporator ices up faster and is defrosted more often, usually with electric heaters. Frozen food has to stay at −18 °C or colder, also while the evaporator defrosts.

Display fridge

A chilled or frozen display unit in a shop where goods are on show for customers, such as a multideck, a serve-over counter or a chest freezer. It can be connected to a central rack (remote) or have its own unit (plug-in). Open display fridges are sensitive to draughts and warm air in the shop.

Setpoint

The temperature the controller aims for, for example 3 °C in a cold room. The system starts and stops around the setpoint with a small differential. The setpoint has to sit far enough below the limit in your HACCP plan for the food to stay cold through defrosts and door openings.

Controller

The electronic control that switches the compressor, fans and defrost on and off based on sensors and setpoint. The controller can also raise local alarms. Maci Intelligence reads nothing from the controller and is fitted independently of it, whatever the make.

Defrost

The period when the evaporator is warmed so the ice melts and drains away. It is done with electric heaters, hot gas or by simply stopping the cooling, on a schedule or on demand. A defrost that fails leads to icing, and one that runs too long wastes electricity, read about operations.

Icing

Ice building up on the evaporator fins until air can’t get through. The cold room slowly warms even though the system is running. Typical causes are a defrost fault, a door that doesn’t close or a failed fan. See refrigeration breakdown.

High-pressure alarm

The alarm when the pressure on the high side gets too high and the high-pressure switch stops the compressor to protect the system. The cause is often a dirty condenser, a failed fan, too much refrigerant or air in the system. Head pressure usually climbs gradually over days or weeks before the alarm trips.

Low-pressure switch

A pressure switch on the suction side that stops the compressor when the suction pressure gets too low. It protects against running short of refrigerant or with an iced evaporator, and is often also used to start and stop the compressor in normal operation. Frequent low-pressure trips are a sign that something is wrong.

COP

Coefficient of performance: how much cooling the system delivers per kilowatt of electricity. A COP of 3 means 3 kW of cooling for 1 kW of electricity. COP drops when the condenser is dirty, the evaporator iced or the compressor worn, which is why power use often tracks the condition of the system.

Call-out

When a refrigeration technician has to come out of hours, usually at night or at the weekend, because a system has stopped. In a typical Danish example, a call-out is about 15 minutes of work and costs about €360 excluding VAT. Faults seen weeks ahead can be fixed on a planned visit in working hours, see fewer call-outs.

Preventive maintenance

Service on a fixed schedule, for example an inspection once or twice a year, whatever the condition of the system. It catches wear that is visible on the day of the visit, and misses what develops between visits. Read about predictive maintenance.

Predictive maintenance

Service when data shows that a system is starting to fail, before it stops. Maci Intelligence learns each system’s normal behaviour and warns typically 3 to 6 weeks before a breakdown, so the repair can be planned. Closely related to condition-based maintenance. Read about the difference.

Monitoring and data

The words used for measuring refrigeration systems, for alerts, and for the records that go with them: for food safety, for F-gas and for carbon reporting.

Refrigeration monitoring

Continuous measurement of a refrigeration system, so faults are found before they stop it. The simplest form is a temperature probe with an alarm. Maci Intelligence measures current, pressure and temperature at several points on the system every minute and sees when something starts to drift. Read about refrigeration monitoring.

Current draw

The electrical current the compressor and fans draw, measured in amps. It changes when a compressor wears, a valve sticks or the condenser clogs, often long before the temperature does. That makes current one of the most important signals in predictive monitoring.

Baseline

The way a particular system normally runs: how much current it draws, what pressures it holds, and how it responds to defrosts and outdoor temperature. Maci Intelligence learns the baseline of each system and reacts to departures from it, with no fixed limits shared by every system.

Anomaly

A reading or pattern that departs from the system’s baseline, for example a current draw that rises slowly over several weeks. An anomaly is a sign that something is changing, and may not be a fault yet. Maci Intelligence judges how serious it is and how long it is likely to be before a breakdown. Read about AI and data analysis.

Escalation

An alert passing on to the next person on the list if nobody responds within a set time. In the example on Maci’s alerts page it moves on after 2 hours without a response, and the refrigeration company can be on the list as the person on call. See alerts and refrigeration alarms.

Data logger

A small device that stores the temperature at fixed intervals so it can be read out later. A data logger records what happened, but usually gives no alarm in time. See the comparison of solutions.

Product temperature

The temperature of the food itself, as opposed to the air in the cold room. It changes more slowly than the air temperature and is what the legal limits refer to. Maci Intelligence measures both air and product temperature, see temperature logs and HACCP.

HACCP

Hazard Analysis and Critical Control Points: the method food businesses use to find the points where things can go wrong and keep them under control. For chilled food, temperature is almost always a critical control point, with a limit, a check and a plan for when the check fails. The requirement is in Regulation (EC) No 852/2004, see HACCP temperature monitoring.

Own-check

The food business’s own programme for making sure the rules are met, built on HACCP, also called a food safety management system. For chilled and frozen storage it sets out the limits, checks, records and what happens when a check fails. The food authority inspects whether the programme exists and is followed, see HACCP temperature monitoring.

GDP

Good Distribution Practice: the EU guidelines for storing and distributing medicines. GDP requires, among other things, temperature monitoring and records, alarms on excursions and calibrated measuring equipment. Many medicines must be kept at 2 to 8 °C, see hospitals and pharma.

Scope 1

A company’s direct greenhouse gas emissions in its carbon accounts under the GHG Protocol. Refrigerant lost through leaks counts towards scope 1, converted to CO2 equivalent. Maci Service produces a scope 1 report from the F-gas log, see ESG reporting.

Questions and answers