Opening sealed compressor housing is an extreme measure that experienced craftsmen resort to when standard methods of diagnosing or replacing a valve group are impossible without dismantling the casing. Most often, the need to cut sealed "pot" occurs when the compressor is filled with freon, the piston group is jammed, or when trying to convert the unit into a powerful air compressor for painting work. This is a dirty, noisy and potentially dangerous procedure that requires strict adherence to safety precautions.
Before using an angle grinder or a hacksaw, you must completely remove the refrigerant from the system. Freon Under pressure it can be dangerous to the eyes and skin, and upon contact with an open flame or hot metal it forms toxic compounds. The process requires careful preparation of the workplace, since there is compressor oil inside the unit, which, when splashed, will create an oil film on all surrounding objects. If you are not confident in your abilities, it is better to replace the entire assembly with a new one.
There are several methods of opening sealed casing, and the choice of tool depends on the availability of equipment and skills. The most common method is to use an angle grinder (grinder) with a thin metal cutting disc. However, this method requires pinpoint precision: one wrong movement, and the disk will damage the internal winding of the electric motor or itself, after which restoration will become meaningless. An alternative is to drill out the weld points or use special sheet metal shears, but these methods are more labor-intensive. rotor, after which recovery will become meaningless. An alternative is to drill out the weld spots or use special sheet metal snips, but these methods are more labor intensive.
⚠️ Attention! It is strictly forbidden to open the compressor without first releasing the pressure in the system and removing the oil. Residual pressure can knock out the plug or cause hot oil to splash when the metal is heated by the tool.
Preparation of the workplace and necessary tools
To successfully carry out the operation cutting the compressor a specialized set of tools will be required. The main tool, of course, is angle grinder (grinder) with a disk diameter of 115 or 125 mm. It is important to use thin cutting discs no thicker than 1mm to minimize heating of the metal and reduce the risk of accidental damage to internal components. You will also need pliers, a hammer, a set of screwdrivers and a container for draining used oil.
Operator safety comes first. When cutting metal, small hot particles are generated, and if there is oil residue, light smoke is possible. Therefore, a mandatory element of equipment is protective glasses that fit tightly to the face and a respirator. Work should be carried out in a well-ventilated area, ideally outside or in a garage with an open gate. The floor must be covered with rags or cardboard, since it will not be possible to avoid drops of oil.
- 🛠️ Angle grinder with thin discs for metal.
- 🥽 Safety glasses and a respirator against oil mist.
- 🧤 Thick work gloves for protect your hands from cuts.
- 🗑️ Container for draining old compressor oil.
- 🔧 Pliers and a set of keys for removing tubes.
Before starting work, you must remove all copper tubes suitable for the housing. They are carefully bitten off with wire cutters or sawed off, trying to prevent metal shavings from getting inside the system. If the compressor was previously removed from the refrigerator, make sure that the process pipe (filling tube) is open or cut off to prevent the formation of vacuum or pressure when the case heats up.
Technology for safe cutting of the body
The most critical stage is the direct cutting of the weld seam connecting the upper and lower bowls of the body. Weld joint usually located in the middle of the side surface of the "pot". The main task is to cut through the metal in a circle without touching the internal components. The cutting depth must be strictly controlled: the thickness of the body wall is about 1.5–2 mm, so the cutting depth should not exceed 2.5 mm.
Start cutting from the top of the seam, making small intermittent movements. Do not press too hard on the tool, allowing the blade to work on its own. Move around the circle, gradually going deeper. It is important to periodically stop and let the metal cool so as not to overheat the insides of the compressor, especially if it is planned to be used further as air compressor. Overheating can warp valve plates or damage winding insulation.
⚠️ Attention! If you feel the blade sink deeper than usual or hear a ringing noise against internal parts, stop cutting immediately. It is likely that the internal baffle or winding is too close to the wall at this point. Shift the cutting line or proceed to sawing in another place.
After the circular cut is made around the entire perimeter, do not rush to tear off the top cover. There may be a jumper or burr inside that holds the structure. Gently tap the seam (through the wood spacer) with a hammer to loosen the joint. If the cover does not come off, check to see if the circle is complete. Sometimes it is necessary to make a second, deeper pass in the thickest places of welding.
☑️ Control of the cutting process
Dismantling the internal mechanical part
After removing the top cover, the internal structure of the unit will open in front of you. The central place is occupied electric motor with the rotor and stator, as well as the crank mechanism, immersed in an oil bath. To remove the mechanical part (piston group), it is necessary to unscrew the three bolts securing the engine to the spring suspension inside the casing. These bolts are located symmetrically around the central axis.
The “filling” should be removed extremely carefully, lifting it strictly vertically. The mechanism is heavy and can be lubricated with thick oil, so it can slip out of your hands. It is best to place a soft rag underneath. At this stage, the cause of the malfunction, if there was one, becomes visible: a broken connecting rod, a torn cylinder-piston group or burnt winding. To convert it into an air compressor, this unit is often left assembled, changing only the valves.
- 🔩 Unscrew the three bolts securing the engine to the springs.
- 🔌 Carefully disconnect the power wires from the terminals.
- 🏗️ Remove the cylinder block together with the engine upwards.
- 💧 Let the remaining oil drain into the prepared container.
If your goal is to repair valves, then after removing the cylinder block you need to unscrew the cylinder head. Underneath it you will see thin metal plates - suction and discharge valves. Often it is their deformation or breakage of the tongue that causes the compressor to hum but not create pressure. Replacing these plates with new ones or made of elastic steel (for example, from a probe) can revive the unit.
Why does the valve break?
Most often the valve breaks due to water hammer when liquid freon or oil gets into cylinder at the moment of compression. Also, the reason may be loosening of the cylinder head mounting bolts or factory defects in the metal plate.
Features of conversion to an air compressor
Many craftsmen cut the body precisely in order to use refrigeration compressor as a source of compressed air. This is a popular solution for garage needs, but it has its own nuances. Unlike specialized air units, refrigeration models are not designed to work with atmospheric air containing moisture, which leads to oxidation of internal parts.
When remodeling, it is critical to change the oil. Standard refrigeration oil is hygroscopic (absorbs moisture) and upon contact with air quickly loses its properties, forming acid. To work in an open circuit, it is necessary to use one synthetic compressor oilthat does not absorb moisture, or change it regularly. You will also need to install a filter on the inlet pipe to prevent dust from getting inside the cylinders.
| Parameter | Refrigeration mode | Air compressor mode |
|---|---|---|
| Gas type | Freon (R134a, R600a) | Atmospheric air |
| Outlet pressure | Up to 15-20 Bar | Up to 6-8 Bar (optimal) |
| Oil type | Mineral/Synthetic (POE) | Compressor (not hygroscopic) |
| Cooling | Natural (freon circulation) | Forced (fan required) |
Another important aspect is the cooling system. In the refrigerator, the compressor is cooled by circulating freon and cleaning oil. When working in air head temperature can reach critical values. Therefore, when converting, it is strongly recommended to install an additional blower fan or even water cooling of the cylinder head if long-term operation is planned.
Diagnostics of faults after opening
An opened compressor allows for a complete troubleshooting of components. First of all, they examine stator windings. They must be clean, without traces of burning, blackening or melted insulation. If the copper has turned black and smells burnt, then the motor must be rewinded or replaced, since an interturn short circuit is inevitable in such cases. The integrity of the windings is checked with a multimeter, measuring the resistance between the contacts.
The second important element is the motor shaft and plain bearings. There should be no deep burrs or wear on the shaft. Bearings (bushings) must ensure smooth rotation without play. If the shaft has a transverse groove at the point of contact with the bushing, this will lead to knocking and rapid jamming. In some cases, the shaft can be ground and repair bushings installed, but this requires turning.
⚠️ Attention! When assembling after repair, ensure cleanliness. One grain of sand caught between the piston and cylinder can damage a repaired compressor within a few minutes of operation. Wipe all parts with a rag soaked in solvent.
The condition of the valve group is also checked. The plates must be perfectly flat and fit snugly against the seat. A leak test can be done by assembling the cylinder head and trying to blow air through the inlet and outlet pipes. At suction, air should flow freely in one direction and be blocked in the other, and at discharge, vice versa. Any air suction through a closed valve indicates its leakage.
Assembling and sealing the housing
After repair work or alterations, the question of closing the housing arises. It is almost impossible to weld compressor housing back at home while maintaining tightness and vacuum density without argon welding and special equipment. Therefore, for domestic needs (especially when converting to an air compressor), the housing is often not welded, but is used as an open structure or a removable cover is made.
If you want to maintain the functionality of the refrigeration unit, the top cover can be placed on a sealant and pressed with a clamp, but this is a temporary solution. For a complete restoration, you need to call a specialist with a vacuum pump and solder the process pipe. If the unit is used as an air compressor, an air filter must be installed on the inlet pipe, and a check valve and a receiver (cylinder) on the outlet pipe to stabilize the pressure.
- 🧼 Thoroughly rinse the insides with a solvent to remove shavings.
- 🔩 Install the mechanical part on the springs and secure bolts.
- 🔌 Connect the wires according to the diagram on the terminal box.
- 🔧 Check the free rotation of the shaft before closing.
The final stage is a test run. The compressor should be turned on through a start-up relay corresponding to the engine power. The first start-up should be short-term to ensure that there are no extraneous noises, beatings or oil leaks. If everything goes well, the unit can be operated in test mode, monitoring the heating temperature of the housing.
Can a compressor be used without oil?
There are oil-free compressors, but in refrigeration models, oil plays the role of a lubricant and sealant. Working without oil will lead to instant scuffing of the piston group. However, when converting to air, the oil level must be strictly according to the mark, and not “by eye.”
Frequently asked questions (FAQ)
Is it possible to weld the compressor housing using conventional electric welding?
Theoretically, it is possible, but it is highly not recommended. The high temperature of the arc can damage the varnish insulation of the windings inside, even if you cook carefully. In addition, the thin metal of the case is easy to burn through. It is better to use argon welding or a mechanical connection with a sealant for sealed systems.
What pressure can the piston group of a refrigeration compressor withstand in air?
The standard piston group is designed to work with freon at pressures up to 15-20 atmospheres. However, when working in air, due to the lack of freon cooling and other properties of the gas, pressure up to 6-8 atmospheres is considered safe. Exceeding this limit can lead to destruction of the cast iron or failure of the connecting rod.
Is it necessary to change the oil when remaking the compressor?
Yes, definitely. Mineral oil used in refrigerators quickly oxidizes when exposed to moisture from the air. To operate in an open cycle (atmospheric air intake), a special compressor oil is required that is resistant to oxidation and does not absorb moisture.
Why does the compressor hum, but does not start after assembly?
Most likely, during assembly the gap between the rotor and stator was broken, or the phasing of the windings was mixed up. The cause may also be jamming of the mechanical part due to dirt or improper installation of the connecting rod. Check the free rotation of the shaft manually.