Analysis of faults in compressors, solenoid valves, four-way valves, and refrigeration/heating systems

1. What is Fault and Protection

 

The so-called malfunction refers to the abnormal operation of the air conditioning system, usually manifested as unstable system operation, shutdown, component damage, abnormal vibration, noise, etc.

 

 

The so-called protection refers to when certain parameters in the system reach a certain value, the system will make limited adjustments to the operating parameters within a certain range through its own adjustment ability, in order to achieve a basic stable operating state of the system, thereby avoiding adverse consequences such as component damage and even shutdown.

 

 

Protection is relative, meaning that it has not yet exceeded the normal operating range and the system is attempting to restore it to its normal value by adjusting its own parameters. Protection is achieved through retractable control, which can effectively reduce frequent shutdowns caused by faults

 

 

2. Fault point finding method

 

Outdoor unit:

 

Seven segment code display.

 

Various indicator lights: including power indicator lights, communication indicator lights, etc.

 

Listen, see, touch: Listen for any abnormal sounds or movements of solenoid valves, electronic expansion valves, compressors, etc; Check if the fan is running normally; Check if the temperature of the gas-liquid pipe is normal, etc.

 

 

Indoor unit:

 

Whether the power indicator light, communication indicator light, etc. are flashing normally, whether the indoor fan is running normally, whether the temperature of the gas-liquid pipe is normal, and whether there are other abnormal sounds.

 

 

Wire controller:

 

Check if the switch indicator light is normal and if there are any fault codes displayed.

 

 

 

3. Compressor case and analysis:

 

According to data from a certain manufacturer, the main causes of compressor defects are system impurities and poor fuel supply, accounting for 68% of the total defects 5%, some projects have experienced multiple instances of compressor failure, and there are also serious accidents where three or more compressors on the same machine have failed. These issues indicate that there are significant issues in both the management of the installation process and the control of the compressor replacement process.

 

 

 

 

 

The main defects of the compressor are:

 

Noise; Reverse phase sequence connection;

 

High or low temperature;

 

Overcurrent;

 

Poor insulation.

 

 

Main influencing factors:

 

Power supply issues (power supply phase loss, reverse phase sequence connection, three-phase imbalance of power supply voltage, etc.);

 

AC contactor (capacity selection);

 

Vacuum electrification;

 

Cleaning of refrigeration systems (impurities, non condensable gases, moisture, etc.);

 

Compressor overheating (insufficient refrigerant, high compression ratio, blocked pipelines, poor oil return, etc.);

 

Liquid refrigerant (migration, reflux, liquid hammer, etc.);

 

Refrigerant volume (insufficient or excessive);

 

Refrigeration engine oil (lack, poor oil return, deterioration (affected by moisture and impurities);

 

The impact of other system components (heat exchanger, electronic expansion valve, bypass valve, four-way valve, etc.);

 

The compressor itself is defective (poor insulation, internal impurities, etc.).

 

 

4. Case of reverse phase sequence connection

 

Symptoms of malfunction: After the AC contactor of the compressor is engaged, the compressor does not operate but the current rises quickly and stops for protection; Alternatively, the compressor can operate with high noise, high temperature, and no significant difference in current.

 

 

Cause analysis: Check that the power supply phase sequence is normal and there is no phase sequence protection alarm for the outdoor unit ("05"); Connect the power cord of other compressors to the compressor and it can operate normally, indicating that there is no problem with the compressor; So, it may be a problem with the power supply of the compressor. After inspection, it was found that the S and T at the TB3 terminal block were connected in reverse.

 

 

Processing method: After adjusting the phase sequence, the compressor runs normally.

 

 

Preventive measures: During the maintenance process, pay attention to confirming the phase sequence of each part of the power supply.

 

 

5. Cases of poor oil return

 

Fault phenomenon: When the compressor is running, there is a lot of noise and the exhaust temperature is too high; When running for a long time, the exhaust temperature rises rapidly and quickly reaches the temperature protection state (128 ° C), causing a shutdown and restart. Sometimes, it may directly reach 140 ° C and trigger an alarm shutdown.

 

 

Cause analysis: Check that the compressor exhaust temperature sensor is normal, the refrigerant volume is basically normal, and the return air temperature is normal. Check the oil return pipe, the oil can return, but the oil color is darker. After being left for a period of time, there will be copper shavings and black sludge at the bottom of the oil. So analysis suggests that impurities such as copper shavings in the oil lead to poor lubrication of the compressor, increased mechanical friction, increased noise, and the generation of iron shavings due to friction, further deteriorating the oil quality and ultimately causing damage to the compressor.

 

 

Solution: For repairs caused by system impurities or poor oil return, it is necessary to thoroughly replace the refrigeration oil and blow out the system, clean the gas-liquid separator, oil separator, compressor suction pipe and return pipe, etc.

 

 

Preventive measures: During the installation process, strict requirements are imposed to ensure the cleanliness of the system

 

 

6. Excessive moisture and ice blockage

 

Fault phenomenon: When the compressor is running, the discharge temperature of the compressor is too high, the suction temperature is too low, and the suction pressure is too high; The suction pipe filter is severely frosted and the front and rear frosting are inconsistent, and the bottom of the gas-liquid separator is severely frosted; After shutdown, the frost and melting of the suction pipe after the gas-liquid separator and filter are slower.

 

 

Cause analysis: From the fault to the present

 

 

 

 

 

 

The condensation or dripping phenomenon caused by the low temperature of the liquid pipe is mainly due to the lax closure of the electronic expansion valve. There are several possible reasons for the lax closure of the electronic expansion valve:

 

Abnormal wear of sealing surfaces caused by excessive impurities;

 

The issue with the sealing surface material;

 

Poor control.

 

 

 

7. Fault analysis of four-way valve:

 

Fault phenomenon: The four-way valve does not reverse during refrigeration or heating, resulting in poor refrigeration or heating effect. When feeling the temperature of each pipe of the four-way valve by hand, there is not much difference in temperature among the three pipes below.

 

 

 

Cause analysis:

 

Valve block jamming, insufficient machining accuracy of valve block, or vibration during long-distance transportation; There are foreign objects inside the valve body.

 

Short circuit in the coil, disconnection of the coil or lead of the four-way valve.

 

Substrate Xiaoliang, external machine substrate has no 220V output.

 

Capillary blockage.

 

 

Solution: Replace the coil; Replace the substrate; Strike the valve body; Replace the four-way valve.

 

 

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