Connecting the motor from the refrigerator: diagram, tools and 5 critical errors

An old compressor from a refrigerator is not just scrap metal, but a ready-made electric motor with a long service life that can be adapted for homemade machines, air blowers or even mini-compressors. But you won’t be able to connect it “as is”: you need to correctly identify the contacts, assemble the starting circuit and ensure safety. In this article we will look at step-by-step connection diagramthe necessary tools and typical errors that lead to engine failure.

The main difficulty is that refrigerator compressors (for example, Danfoss, Embraco or Secop) do not have standard terminals for direct connection to a 220V network. Their windings require the correct combination of working and starting capacitors, and in some models even a protection relay. Without these elements, the engine will either not start or will burn out after a few minutes of operation.

Before you begin, make sure that your project really requires a compressor engine. For many tasks (for example, ventilation or mixing liquids), a regular asynchronous motor from a washing machine is suitable - it is easier to connect. But if you need high pressure or tightness (as in refrigeration systems), then a compressor is the best choice.

1. How the refrigerator engine works: 3 key elements

The refrigerator compressor is sealed unit, inside which there is an electric motor and a pump part. On the outside you will see only three terminals (sometimes four), which correspond to:

• 🔌 Common contact (connects both windings)
• 🌀 Working winding (supports rotation after starting)
• ⚡ Starting winding (needed only for the initial push)

In some models (for example, Embraco EG or Danfoss NL) there may be an additional output for the built-in thermal relay, which protects against overheating. If it is not there, the relay will have to be purchased separately.

It is important to understand that the compressor works in oil environment: a special refrigeration oil circulates inside the housing, which lubricates the rubbing parts. If you plan to use it for other purposes (for example, as a vacuum pump), make sure that the oil does not leak out - this will lead to jamming.

⚠️ Attention: If the compressor has been stored in a horizontal position for a long time (for example, after dismantling the refrigerator), wait at least 24 hours in a vertical position before starting it for the first time. This is necessary so that the oil flows from the tubes back into the crankcase.

2. Tools and materials: what you will need for connection

To safely connect the motor from the refrigerator you will need:

• 🔧 Multimeter (for testing windings and checking resistance)
• ⚡ Capacitors: working (25–40 µF) and starting (80–120 µF)
• 🔌 Terminal block or soldering for connecting wires
• 🛠️ Relay protection (if it is not included in the compressor kit)
• 📏 Insulating tape/heat-shrink tube for insulating connections

For starting capacitor suitable model CBB60 or CBB61 on 400–450V. The working capacitor must be non-polar (for example, MKP or MBGO). If you use a polar capacitor (for example, electrolytic), it will explode when connected to alternating current!

Additionally, you may need:

• 🔨 Drill (for attaching the compressor to the base)
• 🧲 Magnetic holder (to fix tools during work)
• 📊 Terminal block on DIN rail (for neat installation of the circuit)

⚠️ Attention: Do not use capacitors from old household appliances (for example, from microwaves or washing machines) without first checking! Their capacity could change due to the electrolyte drying out, which will lead to incorrect operation of the engine or a short circuit.

3. Connection diagram: 3 options for different tasks

There are three main schemes for connecting a compressor from a refrigerator, the choice of which depends on your task:

Scheme 1: Direct connection with a starting capacitor (for short-term operation)

This diagram is suitable for testing a compressor or using it as a manual pump management. The starting capacitor is connected in parallel with the working capacitor only for the startup time (2-3 seconds), then it is turned off with a button. data-i="142">├─[Button]─[Starting capacitor]─[Starting winding]

~220V
│
├─[Run capacitor]─┬─[Common terminal]
│                       │
│ ├─[Work winding]
│
├─[Button]─[Start capacitor]─[Start winding]

Scheme 2: Connection via a relay (for long-term operation)

If the compressor will operate continuously (for example, in a ventilation system), it is necessary to use start-protective relay (for example, Danfoss 103N0012 or Embraco EGX). It automatically turns off the starting winding after the engine accelerates.

~220V
│
├─[Relay]─┬─[Common terminal]
│        │
│ ├─[Working winding]
│        │
│ ├─[Starting capacitor]─[Starting winding]
│
└─[Working capacitor]

Scheme 3: Connection without capacitors (for testing only!)

This method is used to check the health of the compressor, but not suitable for constant operation. Connect the working and starting windings directly to the network for 1–2 seconds. If the engine starts, it is in good condition, but it will not work for a long time (overheating is guaranteed).

For homemade compressors it is most often used second circuit, as it provides reliable starting and protection against overloads. If you are going to use the compressor in a pressure system (for example, for painting), add pressure switch to the diagram (for example, Condor MPR-3), which will turn off the power when the specified level is reached.

How to check the direction of rotation of the compressor?

If after connection the compressor rotates in the opposite direction (determined by sound or air movement), swap the starting winding wires. In some models, the direction of rotation is not critical, but for air blowers it is important - the wrong direction will reduce performance by 30-40%.

4. Step-by-step instructions: how to connect a compressor in 6 steps

Follow these instructions to safely connect the motor:

1. Step 1: Determining the terminals
   

   Ring a multimeter in resistance mode on all three terminals of the compressor. There should be resistance between the common terminal and the working winding; between the common terminal and the starting winding - 10–30 Ohm, between general and starting - 20–50 Ohm. The total resistance of the working + starting windings should be equal to the resistance between the working and starting terminals.

2. Step 2: Selection of capacitors
   

   The capacity of the working capacitor is calculated by the formula: Cp = 2800 * I / U, where I is the winding current (indicated on the compressor nameplate), U is the voltage (220V). For most household compressors, a capacitor is suitable 30–35 μF. The starting capacitor should be in 2–3 times more (80–100 μF).

3. Step 3: Assembling the circuit
   

   Assemble the circuit on the terminal block, observing polarity (for electrolytic capacitors). Connect the starting capacitor via a button or relay.

4. Step 4: Checking the insulation
   

   Make sure that the compressor housing is not energized. To do this, check the resistance between each pin and the metal case - it should be more than 1 MOhm.

5. Step 5: First start
   

   Connect the circuit to the network via 30 mA RCD (required!). Press the capacitor start button for 1-2 seconds. If the compressor starts and runs smoothly (without knocking or vibration), the circuit is assembled correctly.

6. Step 6: Setting up protection
   

   Set the thermal relay to a current that is 20–25% higher than the rated current (for example, if the nameplate indicates 1.2 A, set the relay to 1.5 A).

If the compressor does not start:

• 🔍 Check the correct connection of the windings (possibly working and starting are mixed up).
• 🔋 Make sure that the capacitor capacity corresponds to the calculated one.
• 🔌 Check the voltage in the network - if it is low (less than 200V), the compressor may not start.

5. Typical mistakes and how to avoid them

Even experienced professionals sometimes make mistakes when connecting compressors. common:

• ❌ The use of electrolytic capacitors in an alternating current circuit
  

  This leads to their explosion! capacitors non-polar capacitors (For example, MKP or polypropylene).

• ❌ Connection without a thermal relay
  

  Without overheating protection, the windings will burn out in 10–15 minutes of continuous operation. The relay must be designed for a current exceeding the rated current by 20–30%.

• ❌ Incorrect selection of capacitor capacity
  

  Too large a capacitance will lead to overheating of the windings, too small - to a weak rotation torque. For compressors with a power of 140–180 W, the optimal capacity of the working capacitor 25–35 μF.

• ❌ Ignoring oil starvation
  

  If the compressor was stored horizontally, oil could leak from the crankcase. Before starting, let it sit for days in a vertical position.

Another common problem is vibration and noise operation. This may be caused by:

• 🔧 Loose compressor mount (fix it on rubber shock absorbers).
• 🛢️ Lack of oil (you can only add special refrigeration oil, for example Emkarate RL 32H).
• 🌀 An unbalanced rotor (if the compressor was dropped or subjected to impacts).

⚠️ Attention: If after connection the compressor gets very hot (the housing is hot, it is impossible to hold your hand), turn it off immediately! This is a sign of interturn short circuit or incorrectly selected capacitors. Further work. will lead to irreversible damage to the windings.

6. Practical examples: where can you use an old compressor

Here are several real projects where a compressor from a refrigerator is used:

• 🎨 Compressor for airbrush
  

  Using a receiver (for example, from a fire extinguisher) and a pressure switch, you can assemble a mini-compressor for painting models or small parts. The pressure is adjustable from 1.5 to 3 bar.

• 🐟 Pump for an aquarium or pond
  

  The compressor is connected to the sprayer, creating aeration of the water. It is important to use moisture-proof connections and place the compressor above the water level (to avoid water hammer when turned off).

• 💨 Ventilation/blowing system
  

  If you connect a compressor to a pipe with holes, you will get a powerful air blower for drying or cooling. For example, in a garage for blowing a car after washing.

• 🔧 A vacuum pump for an air conditioner
  

  With the replacement of oil with a vacuum one (for example, Vacuum Oil ISO 15), the compressor can be used. used for pumping freon from air conditioning systems.

For each project you will need refinement of the circuit. For example, for an airbrush compressor you need to add:

• 📉 Pressure reducer (for smooth adjustment)
• 💧 Moisture-oil separator (so that there are no oil particles in the air)
• 🔄 Check valve (prevents pressure release in the receiver)

If you plan to use the compressor in a system with a pressure higher 4 bar, be sure to add safety valve (for example, Wika S111) to avoid pipe rupture.

7. Safety: 5 rules that will save lives

Working with electric motors and pressure systems requires strict adherence to safety precautions:

1. Grounding
   

   The compressor housing must be grounded! If your network does not have grounding, use An RCD with a leakage current of 30 mA.

2. Checking the insulation
   

   Before the first start, check insulation resistance between the terminals and the case (must be >1 MOhm). Use a megohmmeter or multimeter in high resistance mode.

3. Wear gloves
   

   When connecting capacitors, wear dielectric gloves - even after disconnection they can retain a charge.

4. Pressure control
   

   If the compressor is used to pump air, install pressure gauge i safety valve (adjusted to maximum operating pressure + 10%).

5. Fire safety
   

   Do not leave a running compressor unattended. Refrigeration oil is flammable, and overheating of the windings can lead to a fire.

Pay special attention installation location:

• 🚫 Do not place the compressor in damp areas (risk of short circuit).
• 🌡️ Provide ventilation - overheating reduces the engine life.
• 🔇 Install the compressor on vibration mounts (such as rubber gaskets) to reduce noise.

⚠️ Warning: If you smell burning or see smoke from the compressor, do not attempt to extinguish it. water! Turn off the power first, then use a carbon dioxide or powder fire extinguisher. Water conducts electricity and may cause electric shock.

FAQ: Answers to frequently asked questions

Is it possible to connect a compressor from a refrigerator directly to a 220V network without capacitors?

No, this will lead to the engine not starting or burning out. Refrigerator compressors require a phase shift, which is provided by capacitors. The exception is a short-term connection for testing (1–2 seconds), but this also reduces the life of the windings.

Which capacitor to choose if there is no nameplate on the compressor?

For most household compressors with a power of 140–180 W, a working capacitor is suitable 30 μF and a starting capacitor 100 μF. If the engine starts poorly, increase the capacitance of the starting capacitor to 120 µF. For an accurate calculation, measure the winding current with clamps and use the formula: C (μF) = 2800 * I (A) / U (V).

Why does the compressor start, but after 5 minutes it turns off?

It works thermal relay. Reasons:

1. The capacitance of the working capacitor is too high (reduce by 5-10 uF).
2. Insufficient ventilation (install the compressor in a ventilated place).
3. Turn-to-turn short circuit in the windings (check the resistance with a multimeter).

If the relay operates immediately after starting, the compressor itself may be faulty (for example, the piston is jammed).

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

Technically yes, but it is impractical:

• The performance of most household compressors is 5–8 l/min, which is too low for tires (pumping will take 20–30 minutes).
• The outlet pressure rarely exceeds 4–5 bar, and for truck tires you need 7–10 bar.
• Refrigeration oil can get into the hose and damage the nipple.

It is better to use compressor for low pressure tasks (airbrush, water aeration).

How to check if the compressor is working if it does not start?

Follow the following steps:

1. Test the windings with a multimeter (the resistance between the common and working/starting terminals should be 10–50 Ohm).
2. Check the resistance between the terminals and the housing (should be >1 MOhm).
3. Connect the compressor directly to the network for 1-2 seconds (without capacitors). If you hear a click or Attempt to rotate, the windings are in good condition.
4. Check the capacitance of the capacitors (it could have dropped over time).

If all the checks have passed, but the compressor does not start, the piston may be jammed (needs repair or replacement).