Danfoss Compressor Guide: Models, Applications & How to Choose the Right One

The Danfoss compressor is the part of a refrigeration system that circulates refrigerant. It draws low-pressure vapor from the evaporator and delivers it to the condenser at higher pressure. The SC15G, SC18G, and SC21G are among the most requested Danfoss compressors in commercial refrigeration, and all three are single-phase hermetic reciprocating models for R134a systems.

This guide covers what these compressors are used for, how the three models differ, and how to choose the right one for a new system or a replacement.

What Are Danfoss Compressors Used For?

Danfoss compressors are used in refrigeration and cooling systems, from small commercial cabinets to larger installations. The SC range is built for commercial refrigeration. Typical uses include:

• Display cabinets and bottle coolers
• Chest and upright freezers
• Small cold rooms
• Condensing units for shops, supermarkets, restaurants, and catering kitchens

Danfoss also makes larger compressors for bigger refrigeration and air conditioning plants, including the MT64 reciprocating compressor and the SM110 scroll compressor. This article focuses on the SC series because that is what most buyers and technicians want when they search for a Danfoss compressor for a fridge or freezer. For a wider look at compressor types, see our guide to the four types of HVAC compressors.

Danfoss Compressor Size Chart: SC15G vs SC18G vs SC21G

Compressor “size” is normally expressed as displacement, the volume the piston sweeps per revolution. A larger displacement moves more refrigerant and gives more cooling capacity, all else being equal. The figures below come from the Danfoss/Secop datasheets for the 220–240 V, 50/60 Hz universal versions.

*Older SC21G datasheets list the motor as CSR and a wider −35°C evaporating limit. Always check the datasheet for the exact code number on the nameplate. All three models need fan cooling of the compressor in normal use.

SC15G, SC18G, and SC21G: Where Each One Fits

SC15G. The SC15G Danfoss compressor is the smallest of the three, with 15.28 cm³ displacement. It suits smaller cabinets, freezers, and cold storage where the load is modest. It uses a CSIR motor with a start capacitor and relay.

SC18G. At 17.69 cm³, the SC18G Danfoss compressor sits in the middle. It is a common choice for medium-load cabinets, larger freezers and small cold rooms, and for replacing an older compressor of similar capacity. It also uses a CSIR motor.

SC21G. At 20.95 cm³, the SC21G Danfoss compressor is the largest single compressor of the three. It suits higher-load applications such as bigger cold rooms, multi-door display units, and condensing units. The current datasheet lists a CSCR motor, meaning it also uses a run capacitor, so the starting components differ from the SC15G and SC18G.

Which one is right depends on the load, not on which model sounds bigger. An oversized compressor short-cycles and wastes energy, and an undersized one runs continuously and struggles to hold temperature.

Which Danfoss Compressors Use R134a?

The SC15G, SC18G, and SC21G are all R134a compressors in their standard versions. R134a is widely used in medium-temperature refrigeration such as display cabinets, bottle coolers, and small cold rooms, and these compressors work across low, medium, and high back pressure applications within the limits shown above.

Some configurations of the SC18G and SC21G are also listed for R513A, and there is an SC21G variant for R1234yf. These are separate code numbers, so never assume that an R134a compressor is approved for another refrigerant. Check the code number and datasheet.

Do not mix refrigerants or oil types when replacing a compressor. R134a systems with these compressors use POE oil. If you are comparing refrigerants for a project, our R134a vs R410A comparison and the guide to choosing the right refrigerant gas cover the differences.

What Does 1/4 HP Mean in a Danfoss Compressor?

HP stands for horsepower, and one horsepower is about 746 watts. A 1/4 HP compressor therefore has a nominal motor rating of roughly 185 watts.

In practice, “1/4 HP” is trade shorthand for a small compressor, usually found in small fridges, water coolers, and compact display units. Two things to know:

• HP is not cooling capacity. Capacity depends on the refrigerant, the evaporating temperature, and the condensing temperature. Two compressors with the same HP label can deliver different cooling output.
• Danfoss datasheets do not size SC compressors by HP. They give displacement, cooling capacity at rating conditions, and motor data, and HP labels for the same model can vary between suppliers. For reference, the SC21G datasheet lists a 550 W motor size, roughly 3/4 HP.

In the Danfoss range we supply, the Danfoss FR8.5G is the model sold as a 1/4 HP compressor for R134a, 220–240 V, 50 Hz. The SC15G, SC18G, and SC21G are larger compressors. If a customer asks for a “Danfoss compressor 1/4,” confirm the exact model or the code number on the old compressor before quoting.

How to Choose the Correct Danfoss Compressor Size

Work through these points in order:

1. Match the system refrigerant. R134a needs an R134a-approved compressor. If you are unsure what the system runs on, start with our refrigerant selection guide.
2. Application and temperature range. Identify whether the system is low, medium, or high back pressure, and find the design evaporating temperature. A freezer and a bottle cooler need very different operating points.
3. Cooling capacity. Calculate the load, then check the compressor’s capacity at your evaporating and condensing temperatures in the datasheet. Do not select displacement or HP alone.
4. Condensing conditions. Consider ambient temperature and condenser size. The datasheet limits for these models include a 60 °C continuous condensing temperature.
5. Voltage and frequency. Confirm the supply matches the compressor’s rated voltage range. The SC models discussed here are single-phase.
6. Motor type and starting components. CSIR and CSCR motors need different starting components. A mismatch causes hard starting or a burnt-out motor. Check the start and run capacitors against the datasheet.
7. Compressor cooling. Check whether the datasheet calls for fan cooling at your ambient temperature.
8. Replacement requirements. For a like-for-like swap, match the mounting, connection sizes, and positions as well.

Replacement Checklist

• Copy the full model and code number from the old nameplate, not just “SC18G.”
• Confirm refrigerant and oil type.
• Compare tube connection diameters and angles.
• Check the mounting hole pattern and the height of the compressor.
• Replace the relay, capacitor, and overload protector if the datasheet calls for a matching set, and check them if the compressor burnt out.
• Find out why the old compressor failed before installing the new one. Low charge, a blocked condenser, poor ventilation, and a failing capacitor are common causes.

Danfoss Compressor Details to Confirm Before You Buy

Before ordering, have these ready:

• Full model name and code number (for example, 104G8820)
• Refrigerant
• Voltage, phase, and frequency
• Application (low, medium, or high back pressure)
• Displacement or cooling capacity
• Motor type and whether a starter kit is needed
• Whether you need a like-for-like replacement or a new selection

Danfoss Compressor for Fridges and Freezers

“Danfoss compressor fridge” searches usually mean one of two things. For a commercial fridge, freezer, or display cabinet, the SC series is a strong candidate, chosen by capacity and application as above. smaller cabinets, the Danfoss FR series, including the FR6G, FR8.5G, and FR10G, covers light commercial R134a duty at a lower capacity. For a domestic fridge, it is safer to match the exact part from the old compressor’s label than to guess from the model name.

How Much Does a Danfoss Compressor Cost?

There is no fixed price for a Danfoss compressor. The price depends on:

• Model and displacement. Larger compressors cost more.
• Refrigerant and configuration. R134a, R513A, and R1234yf versions carry different code numbers, and 50/60 Hz and voltage variants are priced separately.
• Electrical accessories. Whether the compressor comes with a starter kit, capacitor, relay, or cover.
• Single units and pallet quantities are priced differently.
• Stock and lead time. Locally held stock is often quoted differently from import orders.
• Warranty and supplier terms.
• Exchange rates and VAT.

For an accurate quote, send the model name, code number, and quantity to your supplier.

Which Brand of Compressor Is Best?

No single brand is best for every job. The right compressor is the one that matches:

• The application and temperature range
• The refrigerant
• The required cooling capacity
• The operating conditions, such as ambient temperature
• The system’s electrical supply and component compatibility
• The availability of spares and technical support locally

A well-matched compressor from any reputable manufacturer will outperform a badly matched one from the “best” brand. If the system was designed around a specific brand, replacing it with the same brand and model is usually the least risky option. Our compressor range includes Danfoss, LG, GMCC, Kulthorn, Tecumseh, and other brands, and the same selection logic applies to each, as our guide to choosing a Tecumseh compressor shows.

Danfoss Compressor Supplier in the UAE: What to Check

A few points matter locally:

• Supply voltage. The UAE’s 230 V, 50 Hz single-phase supply falls within the 220–240 V range of these compressors.
• High ambient temperature. The datasheets specify an ambient limit of 43°C and a machine room limit of 48°C, and UAE summer temperatures can exceed this around outdoor condensing units. Ventilation, shade, condenser cleanliness, and correct compressor cooling all matter. A regular coil cleaning and preventive maintenance routine helps here.
• Genuine product and documentation. Ask for the exact model and code number on the invoice, and check the nameplate against it.
• Availability of matching parts. Ask about relays, capacitors, starter kits, and filter driers at the same time, so the job is not delayed. Our guide on choosing spare parts for your HVAC is a useful checklist.
• Confirm what is covered and what evidence is required if a claim is needed.

Practical Advice for Technicians, Contractors, and Buyers

• Never select on HP alone. Use the datasheet capacity at your operating conditions.
• Read the whole nameplate and datasheet, including voltage range, motor type, and cooling requirements.
• Fit a new filter drier whenever you change a compressor.
• Evacuate properly with a vacuum pump and charge by weight within the compressor’s maximum charge limit.
• Protect the system with correctly set high pressure and low pressure
• Use a suitable manifold gauge for the refrigerant when checking pressures. Our gauge buying guide explains the options.
• Check the start capacitor and relay before condemning a compressor that does not start.
• Keep the condenser clean and provide airflow across the compressor. Poor cooling shortens compressor life.
• When you are unsure, send a photo of the nameplate to your supplier before ordering.

Danfoss Compressor FAQs

What are Danfoss compressors used for?

Danfoss compressors circulate refrigerant in cooling systems. The SC series is used in commercial refrigeration, including display cabinets, bottle coolers, freezers, small cold rooms, and condensing units. Larger Danfoss models such as the MT64 serve bigger refrigeration and air conditioning plants.

Which brand of compressor is best?

There is no single best brand. The right choice depends on the application, refrigerant, required capacity, operating conditions, and how well the compressor fits the existing system. For a replacement, the same brand and model as the original is usually the safest option.

How much is a Danfoss compressor?

The price depends on the model and displacement, refrigerant and voltage configuration, included electrical accessories, quantity, stock position, and warranty terms. Send the model name and code number to your supplier for a current quote. You can request one here.

What are the important Danfoss compressor details?

Check the full model and code number, refrigerant, voltage and frequency, phase, application range (LBP, MBP, or HBP), displacement or cooling capacity, motor type, starting components, and compressor cooling requirements.

How do you choose the correct Danfoss compressor size?

Calculate the cooling load, then pick the compressor whose datasheet capacity meets that load at your evaporating and condensing temperatures. Confirm the refrigerant, voltage, and motor type as well. Displacement or HP alone is not enough to size a compressor.

Which Danfoss compressors use R134a?

The SC15G, SC18G, and SC21G in their standard versions, and the FR-series compressors such as the FR10G, are R134a compressors. Some SC18G and SC21G codes are listed for other refrigerants such as R513A, so always check the code number.

What is the difference between the SC15G, SC18G, and SC21G?

Mainly displacement: 15.28 cm³, 17.69 cm³, and 20.95 cm³, respectively. A larger displacement gives more capacity. The SC21G datasheet also lists a CSCR motor, while the SC15G and SC18G use CSIR, so their starting components differ.

Can I replace an SC18G with an SC21G?

Not automatically. The larger displacement changes the capacity and load on the system, and the motor type and starting components differ. Check the system load and the datasheet first, and treat a like-for-like replacement as the default.

Do Danfoss SC compressors work on UAE mains power?

The SC15G, SC18G, and SC21G discussed here are single-phase, 220–240 V, 50/60 Hz compressors, which cover the UAE’s 230 V, 50 Hz supply. Check the voltage range on the datasheet for your exact code number.

Conclusion

Choosing a Danfoss compressor comes down to matching it to the system, not to a label. Start with the refrigerant and application, confirm capacity at your evaporating and condensing temperatures, then check voltage, motor type, and starting components.

The SC15G, SC18G, and SC21G cover a wide share of light commercial R134a work between them, with the main difference being displacement. Work from the code number on the nameplate and the datasheet, and ask your supplier to confirm the match before you order.

Looking for a Danfoss compressor in the UAE?

Al-Imran HVAC & AC Spare Parts is a Dubai-based HVACR supplier that has served the trade since 1993. Send us the model name, code number, or a photo of the nameplate, along with the refrigerant, voltage, and application, and we will help you confirm the right Danfoss compressor and quote it for your quantity.

Browse the Danfoss compressor range or contact our team on WhatsApp at +971 558 747 910 or by email at contact@alimranuae.com.