Connecting the refrigerator compressor to 220V without a relay: step-by-step instructions with diagrams

The refrigerator compressor is the heart of the cooling system, and its direct connection to a 220V network may be needed in a variety of situations: from testing performance to creating homemade installations (for example, airbrushes, paint guns or vacuum pumps). However, simply plugging the plug into a socket will not work - the correct connection diagram is required, taking into account the characteristics of the starting winding and protection against overheating.

Many craftsmen make critical mistakes: ignore starting relay, incorrectly determine the winding terminals or use wires of insufficient cross-section. As a result, the compressor either does not start or burns out within minutes. This article will help you avoid typical problems and connect the unit safely - taking into account its technical characteristics and electrical standards.

We will look at:

• 🔍 How to distinguish the working winding from the starting winding (even without a multimeter)
• ⚡ Connection diagrams for compressors with 3 and 4 terminals
• 🛠️ Step-by-step soldering of contacts and selection of components (relays, capacitors, buttons)
• ⚠️ Critical errors that will lead to motor failure

⚠️ Attention: Winding parameters (resistance, current) may differ depending on the compressor model (Danfoss SC10G, Embraco EG80HLE, Secop etc.). Always check the markings on the unit body or the technical documentation of the refrigerator.

1. Preparation: what you will need for connection

Before taking up the soldering iron, collect everything you need. Without the correct components, the circuit will either not work, or the compressor will only last for a few minutes. Here is the minimum set:

• 🔧 Multimeter (to check winding resistance and circuit integrity)
• 🔌 Wires with a cross section of 1.5–2.5 mm² (copper, stranded)
• 🔄 Starting relay (if you plan to use it in the circuit) or capacitor (for manual starting)
• 🔘 NVD button (normally open starter) - for short-term connection of the starting winding
• 🔥 Heat shrink tube or electrical tape (to insulate connections)
• 🔨 Soldering iron, solder and flux (if you will connect the wires by soldering)

For compressors old model (for example, Soviet refrigerators "ZIL" or "Minsk") may be required reducing transformerif the operating voltage of the windings is below 220V. Check this by the marking on the unit body - there is a pair of values like 127V/220V or 110V/230V.

Key point: if the compressor is removed from an electronically controlled refrigerator (for example, Samsung No Frost or LG Inverter), its windings can be designed to work with a control board. In this case, a direct connection to 220V without modifications will lead to instant combustion of the motor due to the lack of current protection.

2. Definition of winding terminals: where common, run and start

On the compressor housing there are usually 3 or 4 terminals, marked with letters:

• C (Common) - common terminal
• S (Start) - starting winding
• R (Run) - working winding
• CS or CR - combined terminal (less common)

If there is no marking, you can determine the windings by resistance:

1. Measure the resistance between all pairs of terminals.
2. The most high resistance is the sum C-S + C-R (usually 20–40 Ohms for household compressors).
3. The most low resistance — this S-R (starting + working windings, 5–15 Ohm).
4. The remaining output from average resistance is C (common).

Example for a compressor Danfoss NL8FJ:

⚠️ Attention: If the resistance between any terminals approaches zero (short circuit) or infinity (open), the compressor is faulty. Connecting it to 220V is dangerous - there is a risk of fire or electric shock!

What to do if you don’t have a multimeter?

If you don’t have a multimeter at hand, you can determine the windings by the thickness of the wires:

- Thick wire - working winding (R).

- Thin wire - starting winding (S).

- Medium in thickness - general (C).

But this method only works for compressors with 3 terminals!

3. Connection diagrams: 3 terminals vs 4 output

The connection diagram depends on the number of pins on the compressor. Let's consider both options.

Scheme for 3 pins (C, S, R):

• 🔹 Connect C i R directly to the 220V network (phase and zero).
• 🔹 Connect the starting winding (S) via the NVD button parallel to the working winding.
• 🔹 Press the button for 1-3 seconds - the compressor should start.

Scheme for 4 pins (with combined CS pin):

• 🔹 Connect CS i R to a 220V network.
• 🔹 Connect the starting winding (S) through a capacitor (25–40 µF, 450V) to the output C.
• 🔹 After starting, the capacitor can be turned off (in manual mode).

For constant operation (for example, in homemade equipment), it is better to use starting relay from a refrigerator or similar (for example, DANFOSS 103N0010It automatically turns off the starting winding after acceleration). rotor.

- Connections are insulated with heat shrink/insulating tape

- Wires are not twisted or strained

- NVD button is working (closes contact)

- The compressor is fixed (vibration can damage the connections)

-->

4. Selecting a capacitor and relay: technical nuances

If you use capacitor to start (instead of a relay), its capacity is selected according to the formula:

C (uF) = (Istart / U) * 10^6

where:

- Istart — starting current (indicated on the compressor nameplate, for example, 3.2A),

- U —mains voltage (220V).

For most household compressors (Embraco EG80, Secop SC10), a capacitor with 25–40 μF with operating voltage 400–450Vis suitable. Use. lower voltage capacitors (for example, 250V) are dangerous - they explode during voltage surges!

If you decide to use starting relay, pay attention to:

• 🔌 Trigger current (must match the starting current of the compressor).
• 🔄 Relay type: for compressors with a high starting current (for example, Danfoss) relays are suitable PTC or current type.
• 🔧 Compatible with voltage: some relays are designed for 110V and are not suitable for 220V.

5. Step-by-step instructions: connect the compressor to 220V

Consider a universal algorithm for a compressor with 3 terminals (C, S, R):

1. Step 1. Checking the windings

   Make sure that the winding resistance is normal (see section 2). If there is a short circuit or break - the compressor needs to be repaired, not connected!

2. Step 2. Preparing the wires

   Strip the ends of the wires by 10-15 mm. If you solder, tin them for temporary connection. Wago.

3. Step 3. Assembly. circuits

   Connect:

   • 🔌 C → phase 220V,
   • 🔌 R → zero 220V,
   • 🔘 S → NVD button → phase 220V (in parallel C-R).

Step 4. Starting

Press the NVD button briefly (1-2 seconds). The compressor should start with a characteristic hum. If not, check the connections or windings.

For compressors with 4 terminals (CS, C, S, R) the circuit is similar, but the starting winding is connected through a capacitor to C, and not directly to the phase.

6. Typical mistakes and how to avoid them

Even experienced technicians sometimes miss critical points. Here's what you cannot do when connecting:

• ❌ Ignore the starting winding - the compressor will not start or will warm up.
• ❌ Use a capacitor with too large a capacity —this will lead to overheating of the windings.
• ❌ Connect the compressor without grounding —if the insulation breaks down, there is a risk of electric shock.
• ❌ Hold the NVD button for more than 3 seconds —the starting winding is not designed for long-term operation.

The most common mistake is to confuse the working and starting windings. connect S as a working one, the compressor will start, but after 5-10 minutes it will burn out due to overload.

Another nuance: if the compressor hums, but does not start, there are two possible reasons:

1. Insufficient voltage in the network (check with a multimeter).
2. Stuck shaft (try to manually turn the rotor through the pulley).

⚠️ Attention: Compressors with inverter control (for example, from refrigerators LG or Samsung with function Smart Inverter) cannot be connected directly to 220V! Their windings are controlled by a PWM controller, and direct connection will damage the motor.

7. Safety measures: protection from fire and electric shock

Working with electricity requires strict adherence to the rules:

• 🔌 Turn off the power when assembling the circuit (even if you “remember everything”).
• 🔥 Use a circuit breaker at 6–10A in the compressor power circuit.
• 🌡️ Control the case temperature - if the compressor has heated up above 60°C, turn it off immediately.
• 🛡️ Ground the housing (especially if the compressor is installed on a metal surface).

For long-term operation (for example, in a workshop), it is recommended to install:

• 🔄 Thermal relay (for example, KSD301) to shut down when overheated.
• 🔋 Voltage stabilizer (if there are frequent surges in the network).
• 🔊 Sound alarm (in case of an emergency stop).

Important: if the compressor will operate in explosive atmosphere (for example, for pumping flammable gases), use only explosion-proof components sealed boxes for electrical connections.

FAQ: Frequently asked questions about connecting a compressor

Is it possible to connect a compressor without a starting device? relay?

Yes, but only for short-term testing. For continuous operation, a relay or capacitor is required - otherwise the starting winding will burn out.

Why does the compressor hum but does not start?

There are several reasons:

• Insufficient capacitor capacity (for 4-pin models).
• Seized shaft (try turning it manually).
• Low voltage in the network (less than 200V).

Check all options in order.

Which wire to use for connection?

Minimum cross-section - 1.5). mm² for compressors with a power of up to 1 kW. For more powerful ones (from 1.5 kW), take 2.5 mm²The wire must be copper, stranded (for example, PVA 3×1.5).

Is it possible to use a compressor from a refrigerator to inflate tires?

Technically yes, but there are nuances:

• The pressure at the compressor outlet usually does not exceed 8–10 atm (enough for car tires, not for a truck).
• You need to install receiver (a container for smoothing out pulsations) and pressure gauge.
• Oil from the compressor can get into the hose - you need oil separator.

For constant use it is better to buy a specialized compressor.

What to do if the compressor gets very hot after connecting?

Turn it off immediately! Causes of overheating:

• The capacitor capacitance is incorrectly selected.
• High resistance in the circuit (poor contacts, thin wires).
• Mechanical part jammed (wear of bearings, lack of oil).

Check the circuit and condition of the compressor.