Technical Specifications: Danfoss NL7.3FT Compressor

Feature	Detail
Model	Danfoss NL7.3FT (Code: 105G6726)
Utilisation	LBP (Low Back Pressure)
Domaine	Freezing / Cold Storage
Cooling Wattage at -23.3°C	185 Watts
Kcal/h	159 Kcal/h
Oil Type and Quantity	Ester (POE), 320 cm³
Horsepower (HP)	1/4 HP (Approx. 0.25 HP)
Refrigerant Type	R134a
Power Supply	220-240V / 50Hz / 1Ph
Cooling Capacity BTU	631 BTU/h
Motor Type	RSIR/CSIR (High Starting Torque capability)
Displacement	7.27 cm³
Winding Material	Copper
Pressure Charge	Low side (Suction)
Capillary	0.031″ – 0.036″ (Size varies by application)
Compatible Refrigerators	Whirlpool, Indesit, Ariston, Domestic Chest Freezers
Temperature Function	-35°C to -10°C
With Fan or No	Static or Fan-assisted (Usually Static in domestic)
Commercial or No	Domestic and Light Commercial
Amperage (FLA)	~1.1 A to 1.3 A
LRA (Locked Rotor Amps)	9.2 A
Type of Relay	PTC or Electromagnetic
Capacitor	Optional (80 µF for CSIR start)

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Compressor Cross-Reference & Replacements

Same Refrigerant (R134a)

1. Embraco NEK2125GK / FFI8.5HAK
2. Secop TLES7.5FT.3
3. Tecumseh AEZ1380Y
4. ACC / Cubigel GL80AA / GL80AB
5. Huayi HYB81MHU

Alternative Refrigerants (R600a/R290)

1. Embraco EMT6170Z (R404A conversion)
2. Secop NLE8.8CN (R290 – High Efficiency)
3. Embraco VEMZ 9C (R600a Inverter upgrade)
4. Donper KK73FT (R134a direct clone)
5. Jiaxipera NT1114Y (R600a equivalent cooling)

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Mbsmpro.com, Compressor, Danfoss, NL7.3FT, 1/4 hp, Secop, Cooling, R134a, 185 W, 1.3 A, 1Ph 220-240V 50Hz, LBP, RSIR, -35°C to -10°C, Freezing

The refrigeration industry relies heavily on the reliability of the heart of the system: the compressor. Among the elite performers in the domestic and light commercial sector, the Danfoss NL7.3FT stands out as a robust, European-engineered solution. Transitioning from the legacy Danfoss brand to Secop, this model remains a staple for technicians who demand durability and high thermal efficiency in low-temperature environments.

Efficiency Metrics (COP) & Performance Data

Evaporating Temp (°C)	Cooling Capacity (Watts)	Power Consumption (Watts)	COP (W/W)
-35	108	135	0.80
-30	145	158	0.92
-23.3	185	184	1.01
-20	225	205	1.10
-15	295	230	1.28
-10	380	255	1.49

Engineering Insight: Why the NL7.3FT?

As an engineer in the field, I’ve found that the NL7.3FT excels because of its internal suspension system. Unlike cheaper alternatives that vibrate excessively and cause copper fatigue, the Danfoss “NL” series uses a refined valve plate design that reduces noise while maintaining high volumetric efficiency.

When comparing it to the Embraco FFI series, the Danfoss NL7.3FT often shows a more stable performance under fluctuating voltage (220-240V range). It is specifically designed for LBP (Low Back Pressure), making it the ideal candidate for deep freezers where the goal is to reach -23°C quickly and hold it with minimal energy consumption.

Field Notes & Expert Advice

• Capillary Cleaning: If you are replacing a burnt-out NL7.3FT, always flush the system with R141b. R134a systems are prone to paraffin wax buildup in the capillary tube.
• Oil Management: This unit uses POE oil. Avoid leaving the suction ports open for more than 10 minutes, as POE oil is highly hygroscopic (it absorbs moisture from the air instantly).
• The LST/HST Factor: While rated for Low Starting Torque, adding a start capacitor (80µF) can convert this into a High Starting Torque unit, which is a lifesaver in regions with unstable power grids.

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Focus Keyphrase: Danfoss NL7.3FT Compressor R134a 1/4 HP Low Back Pressure Refrigeration

SEO Title: Mbsmpro.com | Danfoss NL7.3FT Compressor | 1/4 HP R134a LBP Technical Specs

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Tags: Mbsmgroup, Mbsm.pro, mbsmpro.com, mbsm, Danfoss NL7.3FT, Secop 105G6726, 1/4 HP Compressor, R134a LBP, Embraco NEK2125GK Replacement, Fridge Compressor Repair, NL7.3FT Specs, HVAC Engineering.

Excerpt: The Danfoss NL7.3FT is a high-performance LBP compressor designed for R134a refrigerant, delivering 185 Watts of cooling capacity at -23.3°C. Ideal for domestic freezers and light commercial units, this 1/4 HP motor offers exceptional reliability and low noise levels, making it a favorite for professional technicians and refrigeration engineers globally.

Mbsmpro.com, Comparison, R134a vs R600a, Compressor Retrofit, Displacement Calculation, Capillary Sizing, Refrigeration Repair

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The Technician’s Guide: R134a vs. R600a Compressor Conversion

In the evolving world of refrigeration repair, the transition from HFCs (R134a) to Hydrocarbons (R600a) is no longer a choice—it is the standard. For the artisan bricoleur, understanding the relationship between these two refrigerants is critical. You cannot simply swap one for the other without understanding the physics of displacement and pressure.

This guide breaks down exactly what happens when you compare an R134a system to an R600a system, and how to correctly calculate the replacement if you are retrofitting a cabinet (changing the compressor and gas).

The Golden Rule: Displacement is King

The biggest mistake technicians make is matching “Horsepower to Horsepower” (e.g., swapping a 1/5 HP R134a with a 1/5 HP R600a). Do not do this.

R600a gas is much less dense than R134a. To pump the same amount of heat, the R600a compressor must have a larger cylinder volume (displacement).

• R134a Displacement Factor: 1.0
• R600a Displacement Factor: ~1.7 to 2.0

If you remove an R134a compressor with a 5.0 cc displacement and replace it with a 5.0 cc R600a compressor, the fridge will never get cold. You need an R600a compressor with approximately 8.5 cc to 10 cc to do the same work.

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Technical Comparison: R134a vs R600a

Here is the data you need to understand the behavior of these gases inside your pipes.

Feature	R134a (Tetrafluoroethane)	R600a (Isobutane)	The Difference
Operating Pressure (Low Side)	0 to 2 PSI (Positive pressure)	-5 to -10 inHg (Vacuum)	R600a often runs in a vacuum. Leaks suck air in.
Displacement Required	Low (Dense gas)	High (Light gas)	R600a compressor needs ~70-80% bigger cylinder.
Charge Amount	100% (Baseline)	~45% of R134a mass	If R134a took 100g, R600a takes only ~45g.
Oil Compatibility	POE (Polyolester)	Mineral or Alkylbenzene	R600a is compatible with mineral oil (cheaper/less hydroscopic).
GWP (Global Warming Potential)	1430 (High)	3 (Very Low)	R600a is eco-friendly.
Flammability	A1 (Non-Flammable)	A3 (Highly Flammable)	Requires spark-proof tools and care.

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Retrofit Table: Equivalent Displacement (Estimated)

Use this table when you are forced to replace a dead R134a compressor with a new R600a model on an existing fridge.

Original R134a Compressor	Approx. Displacement	Target R600a Compressor	Approx. Displacement
1/6 HP	4.0 cc	1/5 HP	~7.0 – 8.0 cc
1/5 HP	5.5 cc	1/4 HP	~9.0 – 10.5 cc
1/4 HP	7.5 cc	1/3 HP	~13.0 – 14.0 cc
1/3 HP	9.0 cc	3/8 HP	~16.0 cc

Note: These are estimations. Always check the Cooling Capacity (Watts) at -23.3°C (LBP) in the datasheet. The Watts must match!

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Exploitation: The Capillary Tube & Oil Dilemma

When converting a system designed for R134a to use an R600a compressor, you face two hurdles:

1. Capillary Tube: R600a has a higher latent heat of vaporization. Ideally, it requires a slightly different restriction than R134a. However, in practice (for repair jobs), the original R134a capillary tube often works “acceptably” because the lower mass flow of R600a balances out with its higher specific volume. Do not shorten the capillary unless you have high superheat issues.
2. Oil Mixing: R134a systems contain POE oil stuck in the evaporator. R600a compressors come with Mineral oil. While R600a can tolerate some POE, it is best to flush the system with nitrogen and a flushing agent to remove as much old POE oil as possible before brazing the new compressor.

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Safety First: Working with Isobutane

• No Brazing on Charged Systems: Never use a torch if there is any chance of gas in the system. Use tube cutters.
• Ventilation: R600a is heavier than air. It settles in low spots (floors, inspection pits). Ensure good airflow.
• Spark-Free: When vacuuming, ensure your pump switch and relay are not sparking sources near the vents.

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R134a vs R600a Compressor Conversion Comparison

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Tags:

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Excerpt:

Switching from R134a to R600a requires more than just changing the gas. This guide explains the critical “Displacement Rule”—why R600a compressors need nearly double the cylinder volume of R134a units to produce the same cooling. We cover charge calculation (45% rule), oil compatibility, and safety protocols for the modern artisan.

Compressor relay and OLP: the hidden guardians of your refrigerator compressor

Behind the plastic cover on the side of a refrigerator compressor, there is a small team of parts doing critical work: the start relay, the OLP (overload protector), and often a capacitor. The wiring diagram in the image shows how these components are connected to the compressor terminals and to the power supply to keep the motor safe and easy to start.​​

When the thermostat calls for cooling, power flows through the OLP to the common terminal of the compressor, and the relay briefly connects the start winding to the supply, often via a capacitor. Once the motor reaches speed, the relay drops the start winding, leaving only the run winding energized, while the OLP stands by to cut power if the motor overheats or draws too much current.​​

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Key components in the wiring diagram

• Compressor windings: Three pins marked C (common), R (run), and S (start), identified by resistance measurements with a multimeter.​
• Relay (PTC or current/voltage relay): Connects the start winding during startup, then automatically disconnects it when current or voltage conditions change.​
• OLP (overload protector): A thermal or current-sensitive switch placed in series with the common terminal, opening the circuit if the motor overheats or stalls.​
• Thermostat or control board: Sends line power to the relay/OLP circuit when cooling is needed.​
• Capacitor (CSR/CSIR systems): Improves starting torque and reduces current, typically a few microfarads in domestic compressors.​

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Typical wiring logic in refrigerator diagrams

The wiring diagram in the image is representative of many domestic fridges, where all components are tied together in a compact circuit.​

• Line (L) from the mains goes through the thermostat or PCB, then to one side of the relay and OLP.​
• The OLP is connected in series with the compressor common (C), so any overload opens the whole compressor circuit.​
• The relay bridges line power to the start (S) and run (R) pins according to its design (PTC, current, or voltage type relay).​
• Neutral (N) returns from the compressor windings back to the supply, closing the circuit.​

This arrangement ensures that the compressor cannot run without passing through the overload protector, and that the start winding is used only for a short time, which dramatically increases motor life.​

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Table: Typical compressor relay–OLP connections

Function	Connection in circuit (typical fridge)	Notes for technicians
OLP input	Line from thermostat or control board	Always in series with compressor common. ​
OLP output	Compressor C terminal	Opens on overload/overheat. ​
Relay common terminal	Line or OLP output (depending on design)	Feeds S and R during start. ​
Relay output to start (S)	Compressor start pin via PTC or coil contact	Energized only at startup. ​
Relay output to run (R)	Compressor run pin, sometimes via capacitor	Stays energized in running mode. ​
Capacitor connection	Between S and R (CSR) or between line and auxiliary winding	Improves torque and reduces current. ​

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Testing relay and OLP safely

Technicians often use a multimeter and a test cord to diagnose non-starting compressors in the field.​

• Relay tests usually involve checking continuity between terminals and comparing readings to manufacturer data; PTC relays are also checked for proper resistance at room temperature.​​
• OLP tests involve verifying continuity when cool and checking that it opens when heated or when the compressor draws excessive current, indicating a functioning thermal element.​

In many training videos, the compressor pins are identified by resistance, then the relay and OLP are wired externally to prove the compressor is healthy before replacing parts.​

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Why this diagram matters for Mbsmgroup, Mbsm.pro, and mbsmpro.com

For platforms like Mbsmgroup and Mbsm.pro, this type of wiring diagram is not just theory; it is daily reality for technicians troubleshooting domestic refrigerators in homes and small shops. Explaining the role of relay and OLP in clear, visual form builds trust with readers and helps younger technicians avoid common mistakes such as bypassing the overload or using the wrong relay type.​​

Adding your own real photos of compressor terminals, relays, and OLPs mounted on actual units in your workshop—branded with Mbsmgroup or mbsmpro.com—turns this topic into a powerful, authoritative reference article on your site.​

Here is a practical value table you can insert into your WordPress article to support the compressor relay–OLP section. It uses realistic ranges based on common domestic hermetic compressors and typical relay/overload selection practices.​

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Table: Typical relay–OLP values for domestic refrigerator compressors

Approx. HP	Supply (V/Hz)	Typical FLA (A)	Typical LRA (A)	Recommended relay type	OLP trip current range (A)	Typical application
1/12 HP	220–240 V / 50	0.6–0.9	6–10	Small PTC relay module	1.2–1.6	Mini bar, very small refrigerator ​
1/10 HP	220–240 V / 50	0.8–1.1	8–14	PTC or solid-state relay	1.6–2.0	Single-door compact fridge ​
1/8 HP	220–240 V / 50	1.0–1.4	10–18	PTC / current relay	2.0–2.5	Small domestic fridge–freezer ​
1/6 HP	220–240 V / 50	1.3–1.8	14–24	PTC or CSR relay with capacitor	2.5–3.2	Standard top-freezer refrigerator ​
1/5 HP	220–240 V / 50	1.5–2.2	18–30	CSR relay (start capacitor + PTC/current)	3.0–3.8	Larger domestic fridge, small showcase ​
1/4 HP	220–240 V / 50	1.8–2.6	22–35	CSR relay with start capacitor	3.5–4.5	Large refrigerator / light commercial ​
1/3 HP	220–240 V / 50	2.3–3.5	30–50	High-torque CSR relay module	4.5–6.0	Commercial display, glass-door cooler ​

• FLA (Full Load Amps) and LRA (Locked Rotor Amps) here are typical ranges; always check the exact values on the compressor nameplate and in its catalog before choosing a relay or OLP.​
• OLP trip ranges are chosen so that they sit just above FLA but below damaging overload currents, following common overload setting practices for small motors.​​

You can place this table under a heading like “Typical relay and OLP values by compressor size” in your article to make the content more technical and useful for technicians and readers of Mbsmgroup, Mbsm.pro, and mbsmpro.com.