Cases of multi-line compressor, four-way valve and electronic expansion valve

September 4, 2023

1. What is a fault?

The so-called fault is that the air conditioning system is abnormal during its operation, which is usually manifested as unstable system operation, shutdown, damaged parts, abnormal vibration and noise.

The fault is absolute, which is beyond the established range, and it is impossible to restore the normal operation of the system only by relying on the adjustment mechanism of the system itself. As long as there is a fault, the system will stop running, and only when the fault is eliminated can the system run.

2. What is protection?

The so-called protection means that when some 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, so as to make the system reach a basically stable operating state, thus avoiding the adverse consequences such as damage to parts and even shutdown.

The protection is relative, which means that it has not exceeded the normal operating range, and the system is trying to restore it to the normal value through the adjustment of its own parameters. The protection adopts retraction control, which can effectively reduce frequent downtime caused by faults.

3, fault point finding method

3.1, outdoor unit

1. Seven-segment code display.

2. Various indicators: including power indicator and communication indicator.

3. Listen, see and touch: Listen for the action sounds or other abnormal sounds of solenoid valves, electronic expansion valves and compressors; See if the fan is running normally; Touch whether the temperature of the gas-liquid pipe is normal, etc.


3.2, indoor machine Whether the power indicator light and communication indicator light 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, etc.


3.3, line controller Whether the switch indicator light is normal, whether there is a fault code display, etc.


4. Compressor case

According to a manufacturer's data, the main causes of compressor defects are system impurities and poor oil supply, accounting for 68. 5% of the total defects. Some projects have repeatedly experienced compressor defects, and there are also serious accidents in which more than three compressors have failed in the same machine. These problems show that there are big problems in both the management of installation process and the control of press replacement process.


Main defects of compressor: Noise; Phase sequence is reversed; High or low temperature; Overcurrent; Poor insulation.


Main influencing factors:

Power supply problems (lack of phase, reverse phase sequence, three-phase imbalance of power supply voltage, etc.);

AC contactor (capacity selection);

Vacuum electrification; Cleanliness of refrigeration system (impurities, noncondensable gases, moisture, etc.);

Overheating of compressor (too little refrigerant, too high compression ratio, blocked pipeline, poor oil return, etc.);

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

The amount of refrigerant (insufficient or excessive);

Refrigerated oil (lack, poor oil return, deterioration (influence of moisture and impurities);

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

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


4.1. Case of Phase Sequence Reversion Fault phenomenon: after the AC contactor of the compressor is pulled in, the compressor does not run but the current rises quickly, and it will stop for protection soon; Or the compressor can be operated but the noise is very high, the temperature of the compressor is on the high side, and there is not much difference in electric current.


Cause analysis: Check the alarm that the phase sequence of the power supply is normal and the outdoor unit has no phase sequence protection ("05"); Connect the power cord of other compressors to this compressor, which can operate normally, indicating that there is no problem with the compressor; Therefore, there may be a problem with the power supply of the compressor. After inspection, the S and T at the terminal block of TB3 are reversed.


Port treatment method: after phase sequence adjustment, the compressor runs normally. Precautionary measures: pay attention to the confirmation of phase sequence of each part of power supply during maintenance.


4.2. Cases of bad oil return Fault phenomenon: when the compressor is running, the noise is very high and the exhaust temperature is high; When running for a long time, the exhaust temperature rises rapidly, and soon reaches the temperature protection state (128 °C), so the machine stops and restarts, and sometimes it directly reaches 140 °C and alarms the machine to stop.


Cause analysis: Check that the compressor exhaust temperature sensor is normal, the refrigerant quantity is basically normal, and the return air temperature is normal. Check the oil return pipe. The oil can return, but the color of the oil is dark. After a period of time, there will be copper chips and black sludge at the bottom of the oil. Therefore, it is considered that impurities such as copper chips in the oil lead to poor lubrication of the compressor, intensified mechanical friction and increased noise, and at the same time, iron chips will be generated due to friction, which further worsens the oil quality and eventually leads to the damage of the compressor.


Treatment: For the maintenance due to system impurities or poor oil return, the refrigeration oil and purging system must be completely replaced, and the gas-liquid separator, oil separator, compressor suction pipe and oil return pipe must be cleaned.


Precautionary measures: During installation, strict requirements are required to ensure the cleanliness of the system.


4.3, excessive moisture, ice jam Fault phenomenon: When the compressor is running, the exhaust temperature of the compressor is high, the suction temperature is low and the suction pressure is high; Frosting of suction pipe filter is serious and inconsistent, and frosting at the bottom of gas-liquid separator is serious; After shutdown, the frosting of the gas-liquid separator and the suction pipe behind the filter melts slowly.


Cause analysis: From the fault phenomenon, it may be caused by poor air return caused by serious filter throttling, and the main reasons for serious filter throttling are dirty blockage, ice blockage or filter screen falling off. After the filter is removed, the filter screen is clean and there is no shedding phenomenon, and there is water in the elbow of the suction pipe of the compressor. After the oil and gas oil are poured out, there are white water droplets at the bottom of the oil. Therefore, it can be judged that the main reason for the abnormal parameters of the press is ice blocking, that is, the system moisture exceeds the standard.


Treatment method: Recover the refrigerant, replace all the refrigerating machine oil, install drying filters on the liquid pipe and trachea respectively, and keep the vacuum for 24 hours after vacuumizing. If the pressure rises, keep vacuumizing until the pressure does not rise. After filling refrigerant as required, run. After every 15min, 30min, lh, 2h and 5h, observe the color change of the drying agent and replace it until the color does not change. Precautionary measures: during installation, strict requirements are required to ensure the dryness of the system.


7, electronic expansion valve fault analysis

Failure phenomenon: the evaporator frosted when the internal unit was not turned on (other internal mechanisms in the same system were running cold). Dismantle the internal unit panel, listen to the obvious sound of running water on the evaporator, touch the temperature difference between the steam pipe and the liquid pipe by hand, power off the internal unit and then power on it. When the coil of the electronic expansion valve is reset, the internal mechanism is turned on cold, and the refrigeration is normal. It is judged that the electronic expansion valve of the internal unit is not closed properly and there is steam leakage.


latest company case about Cases of multi-line compressor, four-way valve and electronic expansion valve  0


The phenomenon of condensation or dripping caused by the low temperature of the liquid pipe is mainly caused by the lax closing of the electronic expansion valve. The reasons for the lax closing of the electronic expansion valve are as follows: Abnormal wear of sealing surface caused by excessive impurities; Problems in the material of sealing surface; Poor control.

latest company case about Cases of multi-line compressor, four-way valve and electronic expansion valve  1

8, four-way valve fault analysis

Fault phenomenon: the four-way valve does not reverse when cooling or heating, resulting in poor cooling or heating effect. When you feel the temperature of each tube of the four-way valve by hand, there is little difference in the temperature of the following three tubes.

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Cause analysis:

The valve block is stuck, the processing accuracy of the valve block is not enough, or it vibrates during long-distance transportation; There are foreign objects in the valve body. The coil is short-circuited, and the coil or lead of the four-way valve is disconnected. The substrate is small and good, and the external machine substrate has no 220V output. Capillary blockage.