How to turn a refrigerator engine into a compressor: a step-by-step guide with diagrams

An old refrigerator that has served its life in the kitchen is often sent to a landfill - but its heart, the compressor unit, can get a second life. A motor from a refrigerator, if properly modified, can become a full-fledged motor for inflating tires, operating an aquarium aerator, a paint gun, or even a mini-sandblaster. However, not every engine is suitable for such tasks, and incorrect connection can lead to an explosion of the receiver or failure of the equipment. low pressure compressor for inflating tires, working with an aquarium aerator, a paint gun or even a mini sandblaster. However, not every engine is suitable for such tasks, and incorrect connection can result in an explosion of the receiver or equipment failure.

In this article we will analyze real possibilities refrigeration compressors (brands Danfoss, Embraco, Secop and domestic), their technical restrictions, connection diagrams to receivers from fire extinguishers or gas cylinders, and we will also calculate what pressure they are capable of producing. We will separately dwell on critical mistakesthat beginners make - from the wrong oil to ignoring the check valve.

If you are planning to assemble a compressor for a garage or workshop at minimal cost - this guide will help you avoid typical problems. But remember: even a properly assembled refrigeration compressor unit will not replace an industrial screw or piston compressor in terms of performance and service life. Its niche is tasks with pressures up to 8–10 atm and low air consumption.

1. Which refrigerator motor is suitable for conversion into a compressor?

Not every motor from an old refrigerator is suitable for recycling. Main selection criteria:

• 🔧 Compressor type: only piston (most household models) or rotational (less often). Spiral and centrifugal ones are not suitable for homemade products.
• 📏 Power: optimally 120–180 W (motors from Soviet refrigerators "ZIL", "Biryusa" or "Atlant"). Low-power ones (up to 100 W) will not even handle the aerator.
• 🛢️ Oil condition: if when tilting the compressor from black slurry with metal shavings flows out of the pipe - the engine is worn out and is only suitable for spare parts.
• 🔌 Voltage: most household compressors are designed for 220 V, but there are models for 12 V (car refrigerators) or 380 V (industrial).

The best candidates for conversion are compressors from refrigerators Stinol, Indesit (series CA), Samsung (models before 2010) and domestic "Saratov" or "Orsk". Their easily identified by its characteristic shape: a cylindrical body with three tubes (suction, discharge and service port).

⚠️ Attention: Compressors from modern refrigerators with a system No Frost often have built-in electronics controls, which complicates their adaptation. Before disassembling, check for the presence of a separate starting relay - without it the motor will not start.

2. Technical characteristics: what pressure can a refrigeration compressor produce?

The main question that worries homemade workers: how many atmospheres is it capable of? supercharge the motor from the refrigerator? The answer depends on the model, but on average the parameters are:

It is important to understand that passport pressure (indicated on nameplate) and real working pressure in a homemade compressor are different things. For example, the motor from Danfoss NL8F in the refrigerator creates a pressure of up to 15 atm, but when connected to a receiver without a cooling system, it will have to be limited to 8 atm so as not to overheat.

To calculate the required pressure, use the formula:

P_max = (P_passport × 0.7) – 1 atm

where 0.7 — safety factor, and 1 atm is the minimum pressure for stable operation of the check valve.

⚠️ Attention: If you plan to use a compressor for painting, please note that most spray guns require a pressure of 2.5–4 atm at a flow rate of 150–200 l/min. A refrigeration compressor with a capacity of 10–15 l/min simply will not cope with this task - the paint will lie unevenly.

3. Connection diagrams: how to properly connect the compressor to the receiver

The main mistake of beginners is direct connection of the compressor discharge tube to the receiver. leads to:

• 💥 Hydraulic hammer (if there is oil or condensate left in the system).
• 🔥 Motor overheating (due to the absence of a check valve, air returns to the compressor).
• ⚡ Insulation breakdowns (if the receiver is not grounded).

The minimum required connection diagram includes:

1. A compressor with a start relay.
2. Check valve (for example, 1/4" NPT on 10 atm).
3. Receiver (fire extinguisher, gas cylinder or homemade tank from a pipe).
4. Pressure gauge (preferably two: at the inlet and outlet).
5. Moisture-oil separator (can be made from a coarse filter for water).
6. Safety valve (adjustable to a pressure 10% higher than the operating one).

Typical diagram for a compressor from a refrigerator Stinol-101:

[Compressor] → [Check valve] → [Moisture-oil separator] → [Receiver]
↓
[Safety valve]
↓
[Pressure gauge + Reducer]

⚠️ Attention: Never use plastic canisters or propane cylinders as a receiver, even at a pressure of 3 atm. Acceptable options:

• 🔥 Fire extinguishers OU-2, OU-5, OU-10 (pre-washed from powder).
• 🛢️ Gas cylinders (after removing condensate and checking for leaks).
• 🔧 Homemade receivers made of steel pipes with a wall thickness of ≥3 mm (certification required!).

Make sure that there are no dents or corrosion on the body|

Check the threaded connections for tightness with a soap solution|

Install a safety valve with an operating pressure 10% higher than the operating pressure|

Ground the receiver (especially if it is metal)|

Paint the receiver with heat-resistant paint (to protect against condensation)-->

4. Step-by-step instructions: how to assemble a compressor from a refrigerator with your own hands

For assembly you will need:

• 🔧 Compressor from a refrigerator (for example, Danfoss SC10G).
• 🔌 Start relay (if it is not on the motor).
• 🛠️ Receiver (fire extinguisher OU-5 or gas cylinder 5 l).
• 🔩 Fittings and hoses (rubber or copper, 6–8 mm in diameter).
• 📏 Pressure gauge (up to 10 atm) and reducer (for example, Fubag AR4).
• 🔧 Check valve and moisture separator.
• 🔌 Wires, plug, 10 A automatic machine.

Step 1. Preparing the compressor

Remove the starting relay (if it is external) and check the resistance of the windings with a multimeter:

• Between C (common) and S (starting winding): 20–40 Ohm.
• Between C and R (working winding): 10–20 Ohm.
• Between S and R: the sum of the two previous values.

If the resistance tends to zero or infinity, the windings are shorted or broken.

Step 2. Modification of tubes

There are three tubes on the compressor:

• 🔵 Suction (thick, with a filter) - connected to the atmosphere or air intake.
• 🔴 Discharge (thin, often with a bend) - goes to the receiver through a check valve.
• ⚪ Service (soldered) - used for refilling freon, in homemade the compressor is not needed.

Carefully cut the discharge tube with a grinder or a hacksaw, then cut a thread 1/4" to connect the fittings. The suction tube can be left as is or extended with a hose with a filter (for example, from vacuum cleaner).

Step 3. Assembling the system

Assemble the circuit in the following order:

1. Connect the discharge tube to the check valve (the arrow on the valve should point towards the receiver).
2. Install moisture separator after the valve.
3. Connect the moisture separator to the receiver via an adapter.
4. Mount a pressure gauge and safety valve on the receiver.
5. Connect a pressure switch (optional, but recommended for automatic shutdown).

Step 4. First start-up

Before the first start:

1. Check all connections with a soap solution (there should be no bubbles).
2. Pour fresh oil into the compressor (through the service tube, if it is open).
3. Connect the system to the network via a 10 mA RCD (required!).
4. Start the compressor for 1-2 minutes without load, then check the heating of the housing (the norm is up to 60°C).

5. What kind of oil to pour into the compressor from the refrigerator

Oil in a refrigeration compressor performs three functions: lubrication, cooling and sealing. Using the wrong oil leads to:

• 🔥 Overheating (if the oil is too much). viscous).
• 💧 Leaks (if the oil is too liquid).
• 🛑 Seizing (if the oil has oxidized or mixed with water).

Types of oils for refrigeration compressors:

⚠️ Attention: If you do not know what kind of oil was in the compressor initially, completely drain the old one and fill in universal PAG-46 or POE-32. You cannot mix different types of oils!

How to change the oil:

1. Drain the old oil through the service tube (tilt compressor).
2. Rinse the system with kerosene or a special cleaner (for example, Flushing Agent).
3. Fill in new oil through the suction tube (see the volume in the compressor passport, usually 150–300 ml).
4. Rotate the compressor shaft by hand (so that the oil distributed).

What will happen if you use car oil?

Car oils (for example, 5W-40) are not designed to work with refrigerants and have a high boiling point. In a refrigerator compressor, such oil will quickly oxidize, forming sludge that will clog capillary tubes. In addition, car oils are not compatible with. seals of refrigeration systems (rubber swells or cracks).

6. Typical mistakes and how to avoid them

Even with proper assembly, the compressor can operate unstably or quickly fail. Let's consider the most common mistakes:

• ⚡ No grounding: a metal receiver without grounding is a risk. electric shock if the insulation breaks down. Use a three-core cable with a plug Schuko.
• 🔥 Compressor overheating: if the housing heats up above 70°C, check:
  • Oil level.
  • Cleanliness of the radiator grille (on the compressor).
  • The presence of a check valve (without it, hot air returns to the motor).
• 💧 Condensate in the receiver: if you do not install a water separator, the water will rust the receiver from the inside and spoil the pneumatic tool. Minimum - drain the condensate after each. use.
• 🛑 Incorrect. pressure switch: household relays (for example, RDK-1) are not designed for frequent switching. Suitable for a homemade compressor Condor MPC-50 or Fubag ARC-100.

⚠️ Attention: If the compressor starts to “knock” during operation, turn it off immediately! This is a sign:

• Liquid entering the cylinder (water hammer).
• Wear of piston rings.
• Failure of valves.

Further operation will lead to jamming of the shaft.

7. Alternative applications: what else can be made from a refrigerator compressor

In addition to the classic compressor for inflating wheels or painting, the motor from a refrigerator can be adapted for other tasks:

• 🐟 Aerator for an aquarium: connect a discharge tube to the sprayer through a reducer (pressure no higher than 0.5 atm). The productivity is enough for an aquarium up to 200 liters.
• 🎨 Airbrush for artistic painting: you will need a 1-2 liter receiver and an accurate reducer (for example, SATA with a pressure gauge 0–4 atm).
• 🔥 Sandblasting machine: a homemade "sandblast" from a compressor and a plastic bottle is suitable for cleaning small parts (pressure up to 3 atm).
• ❄️ Vacuum pump: if you turn the check valve over, the compressor can be used to pump out air (for example, when preserving food).
• 🚗 Air suspension: for pumping air cylinders in a car (a 5-10 liter receiver and a pressure switch are required).

Each option requires its own modifications. For example, for an airbrush it is critical stable pressure without pulsations - you will have to install an additional damper (can be made from a car shock absorber).

⚠️ Attention: For a sandblasting machine, use only dry sand with a fraction of 0.1–0.3 mm. Wet sand will clog the tubes, and coarse sand will damage the nozzle and the part.

8. FAQ: answers to frequently asked questions

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

Yes, but with caveats:

• For passenger tires (pressure up to 2.5 atm) any compressor with a power of 120 W or more is suitable.
• For truck tires or SUVs (pressure 3-4 atm) you need a motor from 180 W with a 10 liter receiver.
• Inflating time for one tire is 15–20 minutes (due to low performance).

Be sure to install a pressure gauge and pressure switch so as not to overinflate the wheel.

How long can the compressor operate without stopping?

Recommended mode:

• Continuous operation: no more than 20–30 minutes.
• Break: 10–15 minutes (to cool the motor).
• If the compressor overheats (the housing is hot), reduce the operating time to 10 minutes.

For long-term operation, install a blower fan (for example, from a computer power supply) and a temperature relay.

What is the maximum pressure you can get from a refrigeration compressor?

Theoretical maximum:

• Soviet compressors: 6–8 atm.
• Imported (Danfoss, Embraco): 8–10 atm.
• Automotive (12 V): 3–4 atm.

However, in practice the pressure is limited:

• The strength of the receiver (for example, the OU-5 fire extinguisher is designed for 15 atm, but its walls may be worn out).
• Discharge temperature (at a pressure above 8 atm, the outlet air heats up to 100°C, which is dangerous for hoses).

Is it possible to connect a compressor from a refrigerator to a car battery?

Only if it is a compressor from car refrigerator (designed for 12 V). A household compressor from 220 V cannot be connected to a battery - you will need a 220V/12V inverter with a power of at least 300 W.

To connect a 12-volt compressor:

1. Use wires with a cross-section ≥2.5 mm² (to avoid voltage loss).
2. Install a 15-20 A fuse next to the battery.
3. Do not operate for more than 10 minutes - discharging the battery below 11.5 V will shorten its life.

What to do if the compressor does not starts?

Check in order:

1. Power: is there voltage in the socket? Test the cable with a multimeter.
2. Start relay: it should click when turned on. If not, replace the relay or capacitor.
3. Motor windings: measure the resistance (see step 1 in the instructions).
4. Shaft jamming: try turning the shaft by hand (through the pulley). If it doesn’t spin, the compressor is burned out.
5. Pressure in the system: if there is pressure left in the receiver and the check valve is faulty, the motor will not be able to start.

If the compressor hums, but not starts - the problem is in the starting capacitor (needs to be replaced with a similar one in capacity).