Compressor from a refrigerator and receiver: a complete guide to do-it-yourself assembly

An old refrigerator that has served its life in the kitchen can find a second life in the workshop - if you turn its compressor into a full-fledged air unit for painting, pumping tires or pneumatic tools. Together with a suitable receiver (for example, from a fire extinguisher or gas cylinder), such a homemade compressor is capable of delivering pressure up to 8-10 atmospheres, replacing factory models costing tens of thousands of rubles.

In this article you will find step-by-step instructions with photos and diagrams, analysis of the necessary materials, as well as critical safety nuanceswhich are ignored by 90% of homemade workers. We will look at two options for receivers (balloon and non-balloon), methods for adjusting pressure and typical mistakes that lead to breakdowns or injuries. If you already have a refrigerator compressor Danfoss, Embraco or Secop —you are on the right track.

Before you begin, answer the key question: for what tasks do you need a compressor? The choice of receiver, connection diagram, and even the type of oil in the system depends on this. For example, a minimum power will be enough to aerate an aquarium, but a sandblasting machine will require a reinforced design with cooling.

1. Which refrigerator compressor is suitable for conversion

Not every compressor from an old refrigerator is suitable for a homemade air unit. Main selection criteria:

• 🔧 Compressor type: only piston sealed (not rotary!). They are marked as KF, NF or CF y Danfossor EG/EM y Embraco. Rotary models (for example Secop SC15G) are not suitable due to low outlet pressure.
• 📏 Power: optimally from 140 W. Compressors with power 80-120 W (for example, from mini-refrigerators) will produce a maximum 2-3 atm - this is only enough for aeration.
• 🛢️ Oil condition: if you hear a knock when shaking or the oil has turned black/thickened, the compressor requires major repairs. The normal color of the oil is transparent amber.
• 🔌 Voltage: most household compressors are designed for 220V, but there are models for 12V (car refrigerators) or 380V (industrial).

The best candidates for conversion are compressors from refrigerators Stinol, Atlant, Indesit (series C100, C120) or LG (models with index K marked). Avoid compressors from chest freezers - they often run on freon R404A, which is more toxic R134a or R600a.

⚠️ Attention: Compressors from refrigerators Samsung and Bosch recent years (after 2018) may have electronic control boards, which complicate the conversion. Check the presence of a separate starting relay - without it, connection to the network is impossible.

How to check the operation of the compressor before disassembling:

1. Connect it to the network via the starting relay (if it is external).
2. Measure current consumption by clamps: norm for 140-180 W — 1.2-1.8 A. If the current is higher 2.5 A there is an interturn short circuit.
3. Listen to the work: a uniform hum without grinding or vibration is a sign of serviceability.

2. Choosing a receiver: cylinder vs homemade tank

A receiver is a container for storing compressed air, which smoothes out pressure pulsations and reduces the load on the compressor. Without it, the unit will operate intermittently, overheat and quickly fail. Let's consider two options:

Optimal choice for most tasks - gas cylinder for 50 liters (for example, from propane). It can withstand high pressure, has ready-made threaded connections and undergoes mandatory testing at the factory. Fire extinguishers OU-10 or OP-10 are suitable for low-power compressors (up to 200 W), but they need to be modified: cut off the top part, weld a flange for the fittings.

Homemade tanks from pipes or canisters are the riskiest option. Even if you use a thick-walled pipe Ø150 mm with a thick wall 4 mm, without professional welding and hydraulic tests such a receiver may explode. An alternative is purchased receivers from old compressors (for example, from Fubag or Quincy), which are often sold at disassembly sites.

3. Necessary materials and tools

To assemble a compressor with a receiver you will need:

• 🔨 Tools:
  • A grinder or a hacksaw for metal (for cutting a cylinder).
  • Welding machine (if you are making a homemade one flange).
  • Set of wrenches and heads (10-24 mm).
  • Soldering iron with power 100 W (for copper tubes).
  • Pressure gauges 0-10 atm i 0-16 atm (for inlet and outlet pressure).
• 🛒 Materials:
  • Compressor from the refrigerator (see section 1).
  • Receiver (cylinder or fire extinguisher).
  • Pressure switch (RDM-5 or Condor MDR-1).
  • Check valve (brass, on 1/4").
  • Moisture-oil separator filter (can be from an old compressor).
  • Pressure gauges, fittings, adapters (thread G1/4" or G1/2").
  • Copper tube Ø6-8 mm (for connections).
  • Wire cross-section 1.5-2.5 mm², terminals, electrical tape.
  • Oil for compressors (Shell Coreena P 100 or Mobil Rarus 427).

The total cost of materials (excluding the compressor and receiver) will be 2 000–4 000 ₽if you buy everything new. At disassembly or Avito you can find used parts cheaper in 2–3 times. For example, a new pressure switch costs ~1,800 rubles, and a used one costs 500–800 rubles. RDM-5 a new one costs ~1,800 ₽, and a used one costs 500–800 ₽.

Pay special attention oil. motor or transmission oil - it is not designed for high temperatures and pressure in the compressor. Optimal viscosity for home-made units: ISO VG 32 or ISO VG 46. The volume of oil depends on the compressor model (usually 200-400). ml).

The compressor starts and builds up pressure|The receiver is clean and sealed|The pressure switch is working properly (checked with a multimeter)|All threaded connections have a seal (FUM tape or anaerobic sealant)|The filter-moisture-oil separator is washed and dry-->

4. Step-by-step assembly of the compressor with the receiver

The assembly process will be divided into 5 stages. Follow the instructions strictly in order to avoid mistakes.

Stage 1: Preparation compressor

You need to remove all the refrigeration pipes from the compressor and replace them with new ones. Proceed as follows:

1. Cut three pipes (suction, discharge and service) with a grinder. Leave the length 10-15 cm for ease of soldering.
2. Place brass adapters with threads on the remaining pipes G1/4" (for the suction and discharge pipes). Plug the service pipe.
3. Check the oil level through the service port. If necessary, add through. suction tube (use a syringe with a long needle).

Step 2: Installation of the receiver

For a gas cylinder:

1. Cut off the top of the cylinder with a grinder (if you plan to install pressure gauges on top).
2. Weld a flange with holes for fittings or use a ready-made cylinder valve (after removing the valve).
3. Install on the flange:
   • Inlet fitting (from the compressor).
   • Outlet fitting (to consumer).
   • Fitting for pressure gauge.
   • Safety valve (adjustable to 10-12 atm).

For fire extinguisher OU-10:

1. Cut off the top part and remove the internal siphon.
2. Weld a flange with threaded holes or use an adapter from the neck of the fire extinguisher to G1/2".
3. Install the fittings in the same way as the cylinder.

Stage 3: Assembling the pneumatic circuit

Connect the elements in the following order (see diagram below):

[Compressor] → [Check valve] → [Receiver] → [Filter-moisture-oil separator] → [Pressure switch] → [Pressure gauge] → [Consumer]

Use copper tubes for connections - they withstand vibration and pressure better than rubber hoses. Seal all threaded connections FUM tape or anaerobic sealant (for example, Loctite 577).

Stage 4: Electrical connection

Connection diagram for the compressor and pressure switch:

• Phase (L) goes to the pressure switch, then to the compressor.
• Zero (N) is connected directly to the compressor.
• Grounding (PE) mandatory for a metal receiver!
• The compressor starting relay (if external) is connected in parallel to the main circuit.

Example circuit for a relay RDM-5:

[220V socket]
│
L → [Pressure switch (pins 1 and 2)] → [Compressor]
N → [Compressor]
PE → [Receiver housing]

Step 5: Setting and test run

Before the first start:

1. Close the outlet valve of the receiver (so that pressure accumulates).
2. Open the drain valve at the bottom point of the receiver (to remove condensate).
3. Turn on the compressor and observe pressure gauge. When it reaches 6-8 atm the relay should turn off the power.
4. Check all connections for leaks with a soap solution (if there are bubbles, tighten or repack).

⚠️ Attention: When first started, the compressor can work up to 10-15 minutes without stopping - this is normal, since the receiver is filled from scratch. If the unit does not turn off longer 20 minutes, check the settings of the pressure switch or the presence of leaks.

5. Pressure regulation and automation

For the compressor to operate in automatic mode, you need to correctly configure pressure switch and safety valve. data-i="279">or RDM-5 or Condor MDR-1) have two adjusting screws:

• 🔧 Screw P+ (upper): sets the pressure off compressor (maximum pressure in the receiver).
• 🔧 Screw ΔP (lower): sets pressure difference between on and off (hysteresis).

Recommended settings for different tasks:

How to set the relay:

1. Turn on the compressor and wait until it operates (shuts off) at maximum pressure.
2. If the shutdown pressure is too high, loosen the screw P+ counterclockwise.
3. To increase the hysteresis (so that the compressor turns on less often), tighten the screw ΔP clockwise.
4. Check the settings 2-3 times, since after the first cycle the pressure in the receiver may "float".

The safety valve is adjusted separately. It should operate at 10-20% above the maximum operating pressure. For example, if the relay turns off the compressor at 8 atm, set the valve to 9-10 atm. To adjust, use the key and pressure gauge:

[Safety valve] → [Pressure gauge] → [Compressor]

Smoothly tighten the valve adjusting screw until it will begin to bleed air at the required pressure.

How to check the tightness of the system without a pressure gauge?

If you do not have a pressure gauge, you can use a soap solution and a pump (for example, a bicycle pump). Pump air into the receiver to a noticeable pressure (by hand), then apply the soap solution to all connections. Bubbles will indicate leaks. for pressures up to 2-3 atm —for higher values, a pressure gauge is required!

6. Typical mistakes and how to avoid them

Even experienced craftsmen make mistakes when assembling compressors from refrigerators. Here TOP-5 problems and their solutions:

• 🔥 Overheating of the compressor:
  • Cause: lack of cooling or too small receiver (the compressor works without stopping).
  • Solution: install a receiver with a volume of at least 20 l or add a blower fan. The optimal temperature of the compressor housing is up to 60°C.
• 💧 Condensation in the receiver:
  • Cause: there is no moisture-oil separator filter or drain valve.
  • Solution: install a moisture separator in front of the receiver and drain the condensate after each use. Insulate the receiver in the cold season.
• ⚡ Compressor does not start:
  • Cause: the starting relay is faulty, the winding is broken or the network voltage is low.
  • Solution: check the relay with a multimeter (the resistance between the contacts should be 20-50 OhmIf). the winding is broken, the compressor must be replaced.
• 🔊 Strong vibration:
  • Cause: the compressor is not secured or the receiver is on an unstable surface.
  • Solution: install the compressor on rubber shock absorbers (can be from a washing machine). Mount the receiver on a wall or frame.
• 🛑 The pressure switch does not work:
  • Cause: the relay membrane is jammed or the phase/zero connection is incorrect.
  • Solution: disassemble the relay and check the mobility of the membrane. The connection must be strictly according to the diagram (see section 4).

Another common problem is oil in the air line. This is due to:

• Oil overflow into the compressor (the level should be at 1/3 the height of the crankcase).
• Lack of a filter-moisture-oil separator.
• Excessive tilt of the compressor during operation (maximum angle - 15°).

⚠️ Attention: If oil appears in the air, do not use it for painting this will damage the coating. Install an additional fine filter (for example, Festo LFR-D-MINI) or replace the oil with a less volatile one (for example, Klüber Summit NGLI 2).

7. Upgrading a homemade compressor

The basic design of the compressor and receiver can be improved to improve performance and reliability. data-i="367">5 useful improvements 5 useful improvements:

• ❄️ Cooling system:
  • Install a radiator from the car (for example, from VAZ 2108) on the discharge tube. This will reduce the air temperature by 20-30°C and reduce the formation of condensation.
  • Additionally, you can add a fan 12Vconnected in parallel to the compressor.
• 🔋 Automatic control:
  • Connect a timer (for example, Theben TM 24) to limit the time of continuous operation (maximum 30 minutes per cycle).
  • Install the temperature sensor (DS18B20) on the case compressor with automatic shutdown when 70°C.
• 🔧 Quick connectors:
  • Replace the threaded fittings with type fittings "herringbone" (for example, PC4-06) for quick connection of hoses.
  • Use brass tees to connect several tools in parallel.
• 🛢️ Improved filtration:
  • Add a second fine filter (for example, Parker Zander 30-11) to remove oil mist.
  • Install a moisture separator with automatic drainage (for example, SMC AD3000).
• 📊 Remote control:
  • Connect a wireless pressure gauge (for example, TP-MS5) to monitor pressure from smartphone.
  • Use a relay with a Wi-Fi module (for example, Shelly 1PM) to turn it on/off remotely.

One of the most effective improvements is parallel connection of two compressorsThis increases performance without 1.5-2 times purchase of new equipment. Connection diagram:

[Compressor 1] → [Check valve] → [Receiver]
[Compressor 2] → [Check valve] → [Receiver]

Important: both compressors must be of the same power, and the pressure switch must be designed for the total load.

8. Safety rules for operation

A homemade compressor is a source of increased danger. Ministry of Emergency Situations 15% of explosions of household containers occurs due to improper assembly of pneumatic systems. Follow these rules:

• 🔥 Receiver pressure:
  • Never exceed maximum operating pressure receiver (indicated on the tag of the cylinder or fire extinguisher).
  • The safety valve must operate at 10-20% below the maximum pressure of the container.
• ⚡ Electrical safety:
  • Ground the metal body of the receiver. The cross-section of the ground wire is at least 2.5 mm².
  • Use RCD with leakage current 30 mA in the compressor power supply circuit.
  • Do not leave the compressor turned on unattended for more than 1 hour.
• 🧯 Fire safety:
  • Do not use the compressor near open flames or flammable materials.
  • Oil and filters may spontaneously ignite if overheated - keep a fire extinguisher (OP-2) available.
• 👓 Operator protection:
  • When working with pressure higher 6 atm use safety glasses.
  • Do not direct the compressed air stream at skin - this can cause embargo