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1. Diagnosis and handling of compressor failures: 2008-08-13 22:221. How to identify the 3 terminals on the casing of a hermetically sealed compressor? Running terminal (R), starting terminal (S), common terminal (C); the resistance between RS is greater than the resistance between SC, which is in turn greater than the resistance between RC. The resistance between RS is equal to the resistance between SC plus the resistance between RC. It can be determined by using the above rules. It should be noted that the resistance values of the wiring terminals of a three-phase compressor are equal. 2. How to determine if the compressor motor windings are short-circuited? Use a multimeter set to the R×1 range; after zeroing it, measure the resistance between points C-R or C-S of the compressor motor windings. If the resistance value of the measured winding is lower than the normal value, it can be determined that this winding is short-circuited. For a three-phase motor, use two test leads to touch two of the three terminal posts; if the resistance values obtained in the three measurements are identical, it indicates that the windings are in good condition ； If the resistance measured twice is infinite, it indicates that one set of windings is open-circuited ； If all 3 tests yield infinity, it indicates that at least two pairs of windings are open-circuited ； If two out of three measurements show resistance values that are significantly lower than the value obtained in the other measurement, it indicates a short circuit. 3. How to determine if the compressor motor is grounded through its casing? When the compressor motor’s windings come into contact with the casing and become grounded, it is due to damage to the insulation layer inside the winding wires, which causes a short circuit with the compressor casing. This type of fault can cause the fuse to blow, and the compressor motor will not operate. To check for a short circuit to ground, the resistance setting on a multimeter can also be used. First, zero the instrument. Then, press one probe tightly against the common point, and place the other probe on the exposed metal part of the compressor’s process pipe; alternatively, remove a small piece of paint from the enclosure panel in order to take measurements. If the resistance value is very low, it can be determined that the winding or internal wiring is in contact with the casing and thus grounded. 4. How to determine if there is an open circuit in the compressor motor windings? Set the multimeter to the R×1 setting, then zero it. Connect the probes to any two terminals of the windings and measure their resistance value. If the winding value is infinite (∞), that is, if there is no conductance between the terminals of the two windings, it can be determined that this winding is open-circuited. 5. The compressor does not start. ⑴Check whether the compressor overload, pressure switch, and overcurrent protector have tripped or are damaged. ⑵Check the indoor temperature sensor and coil temperature sensor to determine whether there is an open circuit or poor contact in cooling mode, and whether there is a short circuit in heating mode. ⑶Use a multimeter to check whether the compressor relay is engaged. ⑷Wrong wiring. ⑸The compressor is open-circuited or short-circuited. ⑹The compressor capacitor is damaged. ⑺The AC contactor is broken. ⑻Check whether the corresponding pin of the 2003 has an OV output; if there is an OV output, it is a relay issue. If there is no OV output but rather a 11.5V output, then check whether the corresponding pin of the main chip has a 5V output; if so, it is a problem with the 2003, and if not, it is a problem with the main chip. 6. The compressor overheats, causing it to shut down shortly after starting up (the protector activates). Please check whether it is due to: (1) Insufficient or excessive refrigerant; fix any leaks, evacuate the system, add enough refrigerant, or remove the excess refrigerant. ⑵ The capillary assembly (including the filter) is clogged, causing the suction temperature to rise; please replace the capillary assembly. ⑶ Internal leakage in the four-way valve causes malfunction; it is replaced after confirming the damage. ⑷ If there is a fault with the compressor itself, such as a short circuit, open circuit, or ground connection through the casing, the compressor should be replaced after verification. ⑸ The protection relay is faulty; use a multimeter to check whether its contacts are conductive when the compressor is not overheating. If they are not conductive, replace it with a new protector. When replacing the 5528 and 5532 compressors, it is necessary to check the start capacitor and start relay (if either one is damaged, both must be replaced at the same time). ⑹ The high-pressure level is too high, causing the pressure relay to activate; please analyze the cause and take measures to resolve it. ⑺ The condenser has poor ventilation or airflow short circuits; please remove obstacles on the outdoor side and clean the condenser. ⑻ The system contains non-condensable gases (such as air), please evacuate it and refill it. ⑼ The current drawn by the compressor is too high; please identify the cause and resolve it. ⑽ The ambient temperature of the outdoor unit is too high; please keep it away from heat sources and avoid exposure to direct sunlight. ⑾ The compressor’s cylinder is stuck or the shaft is seized. The compressor housing can be struck with a rubber hammer or an iron hammer padded with a wooden block, or the compressor can be started by using parallel capacitors or releasing fluorine under no-load conditions; however, if these methods do not work, the compressor should be replaced. ⑿ The vapor-liquid valve is not fully open. 7. Determination of low compressor efficiency. The decrease in efficiency is caused by wear of the moving parts, which leads to an excessive clearance, or by damage to the intake and exhaust valves, or by breakdown of the asbestos gasket in the cylinder. It is generally manifested by a decrease in exhaust pressure, an increase in suction pressure, and excessively high temperatures in the compressor cylinder head as well as in the suction and exhaust chambers. If a low-pressure gauge and a high-pressure gauge are connected to the intake and exhaust ports of the compressor, then if the exhaust pressure is above 0.6 Mpa while the intake pressure remains at 0 Pa or only reaches a vacuum level of 52.5 Pa or higher, it can be concluded that the compressor’s efficiency is low. 8. Judgment on the compressor’s loss of operational capability. It refers to a compressor that can operate normally, but has lost its ability to draw in and discharge air. First, cut the liquid addition tube of the compressor with scissors; if a large amount of R22 is released, it can be determined that the problem is not due to a R22 leak causing poor cooling. At this point, the suction and discharge pipes of the compressor can be melted off using a welding gun, the compressor can be removed, and it can be started separately. Once the compressor is running, the suction and discharge pressures can be checked by feeling them with your hand. First, check whether air is being drawn in at the intake port; then, check whether air is being expelled from the exhaust port. Block the exhaust port with your hand – if the pressure felt is not significant or no air is expelled at all, it can be assumed that the compressor has lost its functionality. Because during normal operation, the compressor’s exhaust port cannot be blocked with a finger. 9. Why is the current in the compressor motor too high? ⑴There is an inter-turn short circuit in the compressor, but it has not reached the level that would cause the fuse to blow. ⑵The \"secondary friction\" in the compressor damages the smoothness of the friction surfaces, resulting in an increase in the compressor’s power consumption and current levels. However, this does not yet reach the point where the shafts get stuck or the cylinders become jammed, preventing the compressor from rotating. A multimeter can be used to check the insulation resistance of the compressor motor relative to ground; under normal conditions, this value should be above 2 MΩ. If it decreases significantly or approaches zero, it indicates a short circuit. If the insulation resistance to ground is normal, check the resistance values of the starting and operating windings. In the case of inter-turn short circuit, the operating current increases. 10. What are the reasons for difficult startup of three-phase compressor motors? A. The power supply voltage is too low. B. Short circuit in the compressor motor windings. 11. How to eliminate the problems of reduced speed during operation, blown fuse in one phase, and increased current in one phase in three-phase compressor motors? The reason is often that one phase of the compressor motor winding makes contact with the casing and becomes grounded. After removing the ground wire, a voltage tester can be used to check whether the casing is charged. If the casing is charged, unplug the power plug first, then touch the compressor casing with your hand; a warm sensation should be felt in that area of the casing. Please rewind the compressor motor windings or replace the compressor. 12. How to eliminate the \"clunking\" sound emitted by a three-phase compressor motor during operation? The \"thumping\" sound emitted by a three-phase compressor motor during operation is caused by severe imbalance among the three phases; definitely one of the power phases is missing. Please use the voltage function of a multimeter to check; restoring the three phases will resolve the issue. 13. How to eliminate reverse rotation of a three-phase compressor motor? It is caused by a wiring error; swapping any two wires will resolve it. 14. Sequence and precautions for compressor replacement ⑴. The refrigerant (R22) used in air conditioners is a non-flammable gas, but it will decompose when in direct contact with high-temperature flames, producing toxic gases (welding operations are extremely dangerous if the pressure inside the refrigeration system is too high; welding must not be carried out under such conditions). Therefore, before performing the welding operation, the refrigerant in the refrigeration system is slowly released. ⑵. Determine the condition of the lubricating oil and thus the condition of the refrigeration system: Normal, Abnormal. Condition of the oil: Color – Light yellow, Brown: The refrigerant oil has deteriorated due to high temperatures; Black: Wear has occurred or the refrigerant oil has severely carbonized; Yellow-green: Moisture has entered and produced acidic substances. Taste – None, Burnt smell with an irritating taste. (3) When releasing residual refrigerant, do so slowly; doing it too quickly will cause the lubricating oil in the compressor to be expelled. If the compressor is damaged, toxic gases generated by the thermal decomposition of the refrigerant will be released; operators should be aware of this. ⑷. After releasing the refrigerant, remove the electrical plug and components from the compressor. ⑸. Remove the welded parts of the high- and low-pressure connection pipes (a protective layer can be used to prevent the sound-insulating material from being damaged). ⑹. Remove the old compressor. ⑺. Pour out the compressor refrigerant oil to check its color; if the color is abnormal, the system should be cleaned. ⑻. Install a new compressor. ⑼Use a pipe bender to bend the high and low pressure connection pipes into shape, and install the original rubber feet. ⑽. Brazing operation: brazing the joints of the pipes. ⑾. Connect the compressor wires. To avoid incorrect wiring of the terminal connectors, it is necessary to wire according to the circuit diagram. ⑿. The system is evacuated. Sufficient suction time is required to maintain the system’s vacuum level. ⒀. Fluorination, leak detection. Charge fluorine according to the standard amount specified on the nameplate. 15. How to replace a scroll compressor? When replacing a scroll compressor, the refrigerant must be released from both the high-pressure side and the low-pressure side simultaneously; it is prohibited to do so only from the high-pressure side. The axial seal of the scroll plates can cause the refrigerant to remain on the low-pressure side. During welding, in order to prevent an oxide film from forming on the inner wall of the copper tube, nitrogen must be introduced. The duration for which nitrogen is supplied must be sufficient. To check this, a lit incense stick or cigarette butt is placed at another outlet of the nitrogen; if the stick goes out, it indicates that all the air in the system has been removed, and welding can then proceed. Due to the high requirements for vortex compressors, it is prohibited to use the compressor as a vacuum pump to remove air from the outdoor unit’s piping when replacing the compressor or other parts; otherwise, the compressor will be damaged. A vacuum pump must be used for vacuuming. When servicing the indoor unit’s air intake, the system pressure must not be reduced to a vacuum state; it should instead be maintained at a gauge pressure of at least 0.03 MPa. Otherwise, a vacuum will be created in the axial seal of the compressor’s suction side, and improper handling can damage the compressor. 16. What precautions should be taken when moving an air conditioner equipped with a scroll compressor? Vortex compressors are prone to damage when used for refrigerant recovery after machine relocation, as the refrigerant recovery process takes too long. The compressor operates in a vacuum condition for an extended period, resulting in a high compression ratio and a sharp rise in temperature, which leads to its destruction. Therefore, the time required to recover the refrigerant is no more than 3 minutes ； Or observe the changes in the low-pressure gauge; when the gauge reading is between 0.03 Mpa and 0.05 Mpa, continue pumping for another 20–30 seconds ； Or shut down within 20 seconds after an abnormal sound occurs during the recycling process. After moving the unit and reinstalling it, during the trial run, it is necessary to check the low pressure to determine whether refrigerant needs to be added; this low pressure should be maintained between 0.45 Mpa and 0.53 Mpa, depending on climate and temperature conditions. 17. What are the different types of overload protectors for air conditioner compressors? There are mainly 2 types of overload protectors for air conditioner compressors: (1) External overload protector. The external overload protector is held tightly against the compressor’s casing by a spring clip. It is connected in series on the common line through which the full current flows (for a three-phase compressor, it should be connected to two of the three wires). When the compressor is operating under overload conditions, or when the ambient temperature during air conditioner operation exceeds 43°C, or when the compressor is restarted within less than 3 minutes after shutting down, the overload protector cuts off the current, causing the compressor to stop running. The interior of an external overload protector consists of a bimetallic disc (bimetal strip), contacts, terminal pins, and a heating wire, among other components. A heating wire and a bimetallic disc are installed inside the heat-resistant resin base (in some overload protectors, only a bimetallic disc is present, with no heating element). When there is an overcurrent or overheating condition, the bimetallic disc heats up and deforms, causing the contacts to separate and thus cutting off the current, thereby protecting the compressor motor. As the bimetallic disc gradually cools down and returns to its original state, the contacts close, allowing current to flow and enabling the compressor to resume operation. ⑵Buried overload protector. The structure of the embedded overload protector features a temperature-sensing element that directly detects the temperature rise of the motor windings. When the winding temperature rises above a certain value, it cuts off the circuit, causing the compressor to stop operating. Once the winding temperature drops to normal levels, the protector reconnects the power supply, allowing the compressor to resume operation. 18. What are the different types of protective devices for air conditioner compressors? The air conditioner compressor is the most critical component in the cooling system. Abnormal power supply voltages or harsh operating conditions can often cause the compressor to operate under overload conditions. Without protective devices in place to safeguard it, the compressor motor will be damaged. The commonly used protective devices include the following types: (1) Overload protectors. It is mainly used for overcurrent and overheating protection of compressor motors. The housing of the overload protector is in close contact with the surface of the compressor housing. When used with single-phase compressor motors, the protector should be connected in series on the common line through which the full current flows ； When used with three-phase compressor motors, the protector should be connected in series across two of the three phase wires. ⑵Internal protector. It is mainly used in single-phase compressor motors, connected in series on the common wire of the motor windings inside the compressor, to provide overcurrent protection for the compressor motor. ⑶Thermal relay. It is mainly used for line overcurrent protection in three-phase compressor motors. Its two sets of coils are connected in series across two phases of the three-phase circuit. When an overload current flows and for a certain period of time, its protective switch opens. ⑷Inverse polarity protector. It is mainly used in three-phase rotary compressor motors to protect the phase sequence of the three-phase power supply, thereby preventing the compressor from rotating in the opposite direction. In addition, it also has phase loss protection functionality. 19. How does the overload protector for an air conditioner compressor work? Generally, overload protectors have protection functions for both startup and operation. When the compressor starts, a mechanical failure causes the rotor to lock up, resulting in a rapid increase in current. When this current exceeds the rated starting current value, the protector’s contacts open, cutting off the current and preventing the motor’s starting windings from being damaged. When the compressor is operating normally, if the temperature rises too high or the current exceeds the allowable value due to external factors, the protector contacts will also open, cutting off the power supply and thereby preventing the burning out of the motor’s windings. 20. What are the common faults of overload protectors? What is the reason? How to conduct inspections and repairs? Common faults of overload protectors include: burned-out heating wires, damaged contacts, failure of the contacts to return to their normal position after changes in the internal stress of the bimetallic strip, damaged insulation in built-in overload protectors, and faulty contacts. The reasons for overload include: (1) too low supply voltage and poor symmetry of the three-phase voltages. ⑵Extend the low-speed operation time of the compressor motor. ⑶The compressor motor operates under load at a low voltage for an extended period of time. ⑷The cooling medium flow path for the compressor motor is blocked. ⑸The operating temperature is too high. Checking the overload protector can be done with a multimeter. Under normal conditions, the resistance value should be in the range of dozens of ohms; if the resistance value is infinite, it indicates that the overload protector is open-circuited. After a overload protector fails, aside from issues such as poor contact or stuck contacts that can be repaired, other faults are generally not repaired but instead replaced with new units. Once a built-in overload protector fails, it is generally difficult to repair or replace; it must be replaced along with the compressor. In three-phase compressor motors, the three-phase overload protectors used are mostly bimetallic type. The bimetallic strip element is connected in series with the compressor’s contactor coil and the low-voltage (24V) circuit. The electric heating wire is connected in series with the compressor’s contactor and motor terminals (in the power circuit). When the metal strip experiences overheating or overcurrent, the bimetallic strip can disconnect the compressor motor circuit. 21. What is liquid hammer in compressors? Under normal operating conditions, an air conditioner’s compressor draws in refrigerant vapor rather than liquid. However, if too much refrigerant is charged or if the expansion valve regulates the flow rate excessively, the refrigerant does not evaporate completely in the evaporator; as a result, it is drawn back into the compressor in the form of wet vapor or liquid, causing liquid slugging in the compressor. It can cause the valve discs, valve plates, and pistons to be damaged, and in severe cases, the connecting rods may also deform. When liquid slugging occurs, the compressor emits abnormal noises and also vibrates. Liquid slugging can occur if there is too much refrigerant in the cooling system or if an excessive amount of refrigeration oil is used. If the evaporator of an air conditioner does not have adequate ventilation and the cold air cannot be removed, frost or ice will form on the evaporator. This leads to excessively low low-pressure readings, and it can also cause frost to form on the compressor housing, resulting in liquid slugging. This post was last edited by snowdfr on 2009-4-11 15:37.]