Use of old refrigeration unit outside its regular location - a popular solution for workshops, garages and small industries. When the main body of the equipment fails or requires expensive repairs, the compressor itself often remains fully functional and ready to work. That is why the question of how to start a compressor from a refrigerator without a refrigerator worries many home craftsmen who are planning to assemble a compressor installation for painting, inflating tires or airbrushing.
Before you start connecting, you must clearly understand that you are dealing with a device that operates under high pressure and uses an electric current. Sealed motor-compressor requires a specific approach to starting, since standard plugging into a socket without additional switching will only lead to humming and subsequent burnout of the windings. In this article we will analyze in detail the electrical circuit, preparation features and nuances of safe operation.
The main task when starting is to ensure the correct sequence of voltage supply to the working and starting windings of the motor. In normal mode, this is done starting relay, which automatically opens the circuit after gaining speed. Ignoring this element or connecting it incorrectly is the most common mistake made by beginners, leading to equipment failure. We will look at how to recreate this circuit artificially or use standard parts.
Design features and principle of operation
To successfully start the unit, you need to imagine its internal structure. Unlike open compressors, household refrigerators use sealed blockwhere the electric motor and compressor part are located in a single steel casing filled with inert gas or refrigerant vapor. This eliminates the possibility of simply replacing brushes or belts, but ensures a low noise level during operation.
The case usually has three terminals for connecting to the electrical network. They can be soldered into a triangle or placed in a row. Their purpose is strictly defined: one terminal is the common phase, the second is responsible for the starting winding, the third is for the working winding. Identification of contacts is the first and critical step before applying voltage. An error in identifying the contacts can lead to a short circuit.
When working outside the refrigerator, care must be taken that the unit is not tilted excessively, otherwise oil may enter the suction circuit, which is undesirable for some types of compressors, although not always critical for short-term tests.
⚠️ Attention: Casing The compressor heats up to high temperatures during operation (80–100°C and above). It is strictly forbidden to cover a working unit or place it in closed niches without forced ventilation.
To understand the processes occurring inside, it is worth noting the role of the refrigerant. It not only transfers heat, but also participates in cooling the motor windings. When starting “in air” without freon, cooling occurs worse, therefore time cycles of operation should be reduced compared to the standard mode.
What is the difference between an inverter compressor and a conventional one?
Inverter models do not have a classic starting relay and operate over a wide speed range. It is almost impossible to start such a compressor without a native control unit (inverter), since it requires a specific speed control signal, and not just a 220V supply.
Necessary tools and materials
To organize a workplace, you will need a minimum set of tools that most men have. First of all, you need a multimeter to “test” the windings and check the resistance. Without this device, working with the electrical part motor-compressor is unsafe.
You will also need wires with a cross-section corresponding to the current consumption (usually at least 1.5 mm²), insulating tape or heat shrink, and, of course, a 220V power source. If you plan to use the unit constantly, it makes sense to purchase or assemble a simple control button with overload protection.
- 🔧 A multimeter or tester to check the integrity of the windings.
- 🔌 Wires, terminals and insulating materials (cambrics, electrical tape).
- 🛠️ Pliers, screwdrivers and wire cutters for installation work.
- 🧤 Protective gloves and glasses for safety during test runs.
Pay special attention to the quality of connections. Poor contact in the starting winding circuit will lead to heating and burning of the wires. Use soldering or reliable screw terminals, avoiding simple twists that oxidize over time.
Identification of pins and checking windings
The most critical stage is determining which pin on the body is responsible for what. Usually the terminals are marked, but if it is erased or covered with varnish, you will have to use the measuring method. At the end of the compressor you can often see the letters: C (Common - general), R (Run - working), S (Start - starting). In Soviet models, the markings may be Russian: O, R, P.
If there is no visual marking, take a multimeter in resistance measurement mode. We need to find pairs of contacts. There will be some resistance between any two terminals, and the third will be connected to both of them. The resistance between the working and starting windings will be the sum of the resistances of each of them relative to the common wire.
The algorithm of actions is simple: we measure the resistance between all three pairs of contacts.
1. We find the pair with the highest resistance - these are the ends of the starting and working windings. The third, remaining wire will be common (C).
2. Now we measure the resistance between the common wire and the other two.
3. The output with greater resistance is the starting winding (S), the one with less is the working winding (R).
| Pair of contacts | Resistance type | Value (approximate) | Output |
|---|---|---|---|
| Common - Working | Small | 10–30 Ohm | Working winding |
| Common - Starting | Average | 30–60 Ohm | Starting winding |
| Working - Starting | Large (sum) | 40–90 Ohm | Sum of windings |
| Case - Any output | Infinity | ∞ | Insulation intact |
Check for a “breakdown” of the case, we place one probe of the multimeter on the cleaned metal of the case (scratches), the second one on any terminal. If there is any resistance, starting such a unit It is strictly prohibited is an electric shock.
Circuits connections: with and without relay
There are two main ways to start the motor. The first is the “old-fashioned” method, which requires constant monitoring, and the second is automatic, using a standard or analog relay. Let's consider both options, since a relay is not always at hand.
The option with a button (temporary connection is connected to the main wire). We lead the wire constantly. We lead the wire to the starting terminal through a normally open button. Operation diagram: press the button (current is supplied to the starting winding), wait 1-3 seconds for the characteristic hum and acceleration, release the button (the engine continues to operate on the working winding).
Connection diagram with the button:Phase (L) --> General terminal (C)
Zero (N) --> Working terminal (R)
Phase (L) --> Button --> Starting terminal (S)
A more reliable option is to use starting relayIt is put directly on the terminals. compressor. Inside the relay there is a coil connected in series with the working winding, and contacts that open the starting winding when the current increases. This provides automatic start and protection.
When using a relay, it is important to respect its spatial position. The relay body often has an arrow UP or TOPpointing up. If you turn the relay over, the contacts may not open or close, which will lead to combustion of the starting winding.
Features of operation without freon and oil
Starting the compressor “dry”, that is, without refrigerant in the circuit, has its own characteristics. In normal mode, freon, passing through the system, cools the engine. When operating in air (atmospheric), the cooling efficiency decreases and temperature conditions becomes harsher.
The oil inside the compressor does not disappear anywhere, it remains in the crankcase. However, if the compressor lay on its side for a long time, oil could drain into the lines. Before starting, it is advisable to let the unit stand upright for several hours so that the oil flows back into the crankcase.
⚠️ Attention: When operating without a condenser (radiator at the back of the refrigerator), the outlet air will be very hot. Do not direct the air stream at yourself or flammable objects.
If you plan to use a compressor for airbrushing or pneumatic tools, keep in mind that it will pump air along with oil mist. For such purposes, it is imperative to install an oil separator at the output or use special oil-free filters, otherwise the paint will lie unevenly and the tool will quickly fail.
The duration of continuous operation without regular cooling should not exceed 15–20 minutes. After this, be sure to let the compressor cool for 30-40 minutes. Exceeding this time leads to degradation of the oil and thermal expansion of parts, which can cause jamming.
Diagnostics of faults during startup
Even a seemingly serviceable compressor may not start the first time. Most often, the problem lies in a stuck start relay or oxidized contacts. If, when voltage is applied, a hum is heard, but the shaft does not rotate, and after a few seconds the machine knocks out or the thermal protection is triggered, it means that the engine cannot reach operating mode.
Try to gently tap the relay body with the wooden handle of a hammer (with the power off!). Sometimes this helps free a stuck mechanical anchor. If this does not help, it is better to replace the relay - they are inexpensive and are consumables.
Another common problem is a break in the internal thermal protection. In some models it is built into the body, in others it is part of the external “tablet”. You can check it by checking: the resistance should be close to zero. If the circuit is broken, the protection must be replaced or (temporarily) short-circuited, understanding the risks of overheating.
- 🔊 It buzzes, but does not start: The starting relay is faulty or the piston is stuck.
- 🔥 The housing is heating up: Problems with ventilation or breakdown windings.
- ⚡ Knocks out the machines: Short circuit in the circuit or a malfunction of the capacitor (if any).
- 💨 Weak pumping: Wear of the piston group or valves.
If the compressor makes a metallic knock or clanging sound, operation must be stopped immediately. This indicates mechanical destruction of the components inside the containment zone, and such a unit cannot be repaired at home.
Safety precautions and precautions
Operating compressor equipment carries certain risks. Pressure, even atmospheric at the inlet, becomes dangerous when compressed. Never pinch the outlet pipe with your finger to check for pressure - the jet of oil and air can damage your eyes or skin.
Electrical safety is also paramount. Carry out all work on connecting wires only with the power cord completely disconnected from the network. Use sockets with grounding, as static or breakdown voltage may appear on the housing.
When working in a confined area, make sure there is good ventilation. Although there is no freon in the system, oil vapors and possible leakage of residual gases are not good for breathing. In addition, a running compressor creates noise, so using earplug or headphones would be a reasonable solution to preserve hearing.
⚠️ Attention: It is strictly forbidden to open the sealed compressor housing (with a grinder or a hacksaw) at home. There may be residual pressure and refrigerant vapor inside, and sparks from the tool can ignite the oil.
Following these simple rules will allow you to safely and efficiently use your old compressor for new tasks. Remember that proper preparation and understanding of the electrical circuit is the key to successful startup and long service life of your homemade device.
Is it possible to start a compressor without a starting relay?
Yes, you can, using a button or switch to briefly supply voltage to the starting winding. However, this method requires constant operator control and is not recommended for long-term operation, since there is a risk of not “releasing” the button in time, which will burn the starting winding.
Why does the compressor hum, but does not start?
Most likely, the starting relay is faulty (contacts are stuck or the coil is burned out) or the piston is jammed due to thickened oil or mechanical damage. Also, the reason may be insufficient voltage in the network.
What kind of oil should be poured into the compressor during maintenance?
Domestic refrigerators use special synthetic oil (for example, POE) or mineral oil, depending on the type of refrigerant. For compressors using R12/R22 freon, mineral is suitable, for R134a/R600a - synthetic. They cannot be mixed.
How long can the compressor operate without interruption?
In normal mode (as part of the refrigerator), the operating cycle can last up to 40 minutes. When working “in the air” without effective cooling, it is recommended to limit continuous operation to 15–20 minutes, taking breaks to cool down.
Is it dangerous to inhale vapors from the compressor?
Yes, compressor oil vapors and possible refrigerant residues are toxic. You should only work with the compressor outlet open in a well-ventilated area or using an exhaust air exhaust system.