Publish Time: 2023-11-18 Origin: Site
Air source heat pumps are basically divided into electronic control systems, refrigerant systems, and water systems. For after-sales maintenance, it is necessary to establish a very clear and clear after-sales concept and framework, which is to troubleshoot and analyze faults, and cannot blindly apply empiricism. For example, if the customer's machine reports high voltage protection and you arrive at the site and say that the water pump flow is low, you can directly replace the water pump. In fact, this approach is not correct because there are many reasons for reporting high voltage, and different reasons can lead to the same fault. We need to consider all possible causes of high voltage faults and eliminate them one by one.
The problems that arise in the heat pump system can be divided into several aspects: firstly, the refrigerant system, secondly, the electronic control system, and thirdly, the water system. Any type of malfunction cannot be separated from these three situations. So how do we all distinguish whether it is a system problem, an electrical control problem, or a water system problem? At this point, we need to go to the site to see clearly or receive a call to hear the other party describe various parameters, such as high and low pressure, exhaust temperature, return air temperature, coil temperature, and other technical parameters. We can preliminarily determine whether it is a fluorine system problem, an electrical control problem, or a water system problem.
I encountered many issues with high voltage in the system last year. There are several reasons for the high condensation pressure in the system. Firstly, the water flow rate is too small, and the heat and water discharged from the compressor refrigerant to the condenser cannot be carried away. Its exhaust pressure will be high, and the high-voltage switch itself will be damaged. Additionally, the electrical components connected to the high-voltage switch in the electronic control system may be damaged, such as capacitor damage, voltage divider resistance, and chip damage, which may cause high-voltage faults. So how do we identify whether it's a system issue, an electrical control issue, or a water system issue? Here is the simplest method to tell everyone, looking at the boundary between the power outage and startup of the unit.
Last year, I met an ordinary person who said, 'Oh, come and take a look at this high pressure newspaper.'. Before going, I called him and asked him if the high-pressure fault was reported before or after the compressor started? This problem can be basically distinguished and the overall direction of the problem can be determined. If the high pressure is reported after the compressor is started, it is highly likely to be a problem with the water system, or with the system itself, or with the refrigerant system, which is not closely related to the electronic control system. On the other hand, before the compressor starts, even the fan and water pump are not started, and only when the brake is closed, the high voltage starts to sound. Then it is necessary to consider the reason for the electronic control, and focus the investigation on the electronic control system. Another possibility is that the high-voltage switch itself has been damaged.
So before analyzing each fault, everyone needs to broaden their thinking. The problem may be a single problem, and the fault may be the same fault. However, everyone needs to list all the reasons that cause the fault, and then use troubleshooting or intuitive analysis to find the fault, narrow the scope of the fault cause, and then apply the appropriate medicine to the case. To carry out after-sales maintenance, one must have a clear mind and not blindly repair with the three major tools. Some people say that when they encounter a problem, it is a lack of fluorine, and then add fluorine, or adjust the expansion valve to do a good job. It is very unscientific to conduct maintenance without any theoretical basis. Pay attention to details after sales.
So next, we need to discuss the details with everyone, which is very important. For example, let's talk about a high-pressure meter. When the compressor is not started, the pointer of the high-pressure meter will point to a number. After the compressor is started, the high-pressure gauge will rise as the compressor starts and runs, and when it rises, it will rise to a certain extent. Suddenly, with a noise from the compressor, the high-pressure gauge began to drop sharply and then rise sharply, which is an abnormal detail.
The example just mentioned requires everyone to pay attention to collecting all technical parameters of the system during after-sales maintenance, including exhaust temperature, return air temperature, fin temperature, ambient temperature, condensation temperature, evaporation temperature, etc., as well as the circuit of the compressor. We must have a complete set of data for basic data, so that we can analyze and determine the fault location. Therefore, we must pay attention to every detail, Sometimes, for example, some abnormal noise or abnormal temperature. As long as there are any abnormalities in it, we must carefully discover them. Some details can be measured by instruments, such as voltage, current, pressure, and temperature. Some cannot be measured, such as the details that can be heard or seen or touched through our senses. Sometimes, it can bring us twice the result with half the effort in after-sales maintenance.
Next, I will share with you some typical system issues encountered during the after-sales maintenance of coal to electricity conversion in Beijing last year. Firstly, let me share with you an issue of refrigerant leakage. Most of the refrigerant leaks I encounter occur in the tube of the high-pressure gauge. The tube of the high-pressure gauge is a copper capillary tube. Usually, after the exhaust pipe of our compressor comes out, a small hole is made on the side of the exhaust pipe, and this capillary tube is inserted, welded, and then connected to the high-pressure gauge. This is usually the case.
Last year, many high-pressure meters were made of copper tubes. It was due to vibration and resonance that the tubes of the high-pressure tubes were directly broken. It is not about cracking, but simply that after the tubes were broken, they fell there and the refrigerant immediately leaked out. So the positions where it breaks are approximately less than 1 centimeter away from the solder joint, and it is not on the broken solder joint. Most of them break at this position, so when I discovered this commonality, I went to think about it. Why are so many machines breaking in the same place? I need to find out the reason. When we go to repair a machine, it's not about replacing it where it's broken or repairing it where it's broken. During the process of training, it is important to be good at summarizing problems. Why is it always the case that there are problems here? There must be a certain reason for it, it is not a coincidence.
After I discovered this problem, I consulted a friend who understood the production process and ultimately obtained this result. During welding, the metal inside the copper tube undergoes a change in stress due to heating. After the welding gun is burned for a long time, the lattice structure of the metal changes, causing the copper tube to become brittle. On the contrary, the welding seam is continuous, because there are many welding rods on that seam that have melted and piled up thick on top, and it cannot be broken. So the corresponding measures for this fault can be found. The first is to use synthetic hoses like those used in screw machines, which have strong toughness and will not break. This is a situation. So there is another situation where copper pipes can also be used for welding, but during the process of copper pipe welding, the welding time at the welding junction needs to be short and fast, and the heating time for welding gun welding needs to be short. Low melting point welding rods are used, so as not to cause damage to the metal structure of the copper pipe.
So next, let's talk about frost formation. What is the cause of frost formation in the evaporator of the unit? Let me give you a detailed explanation. To summarize the several situations that caused the evaporator of the heat pump system to frost that I encountered in Beijing last year. The first situation is relatively simple. When I arrived at the site, I saw a screw on the coil above the four-way valve of the unit that was not tightened. After a long period of vibration, the screw was loosened and shaken off, causing the coil of the four-way valve to fall off, causing the four-way valve to be unable to change direction during defrosting. So, causing severe frost formation in the evaporator is the first situation.
The second situation, which is also the only one I saw among so many machines last year, is also particularly peculiar. The reason for frost formation is that two sensors on the circuit board are inserted backwards, one is the return air temperature sensor, and the other is the coil temperature sensor. Inserting these two sensors backwards resulted in the expansion valve becoming smaller and smaller. As we all know, the electronic expansion valve control of our machine is controlled by overheating, We control the electronic expansion valve by subtracting the coil temperature from the return air temperature to obtain the evaporation superheat. As we have said, when the heat is high, the electronic expansion valve opens larger, and when the superheat is low, the electronic expansion valve closes smaller.
So, under normal circumstances, it should be the return air temperature minus the coil temperature. Now that it is inserted backwards, it becomes the coil temperature minus the return air temperature, resulting in a negative number. At this point, the electronic expansion valve will close smaller, and the electronic expansion valve will close smaller. The larger the difference between the return air temperature and the coil temperature of the heat pump market watermark, the greater the absolute value of the negative number it subtracts from the reverse value. Therefore, the electronic expansion valve will further close smaller, Finally, the electronic expansion valve was closed very tightly, resulting in severe frost formation in the evaporator.
Of course, some friends may ask me: Why does the electronic expansion valve not report low pressure when it is closed very small? Let me explain this to everyone, because our electronic control program also has a setting for the minimum opening of the electronic expansion valve, which means that when the electronic expansion valve is closed to the minimum opening in any environment or working condition, it will no longer be closed. If it is lower than the minimum opening, it will report low pressure. Therefore, although it does not report low pressure after closing to the minimum opening, But from the outlet of the expansion valve to the evaporator, there is severe frost formation.
So we just talked about the problem of frost formation in the evaporator. So what exactly is the cause of frost formation? Some people say there is less fluoride, while others say there is more refrigerant. I have conducted a separate analysis on the frosting area and will share it with you today. What should I do when I see the evaporator frosting on site? After we go, we first remove the frost, whether through forced defrosting or hot water flushing. After removing the frost, we restart the unit and then observe the process of frost formation to see if it is a normal or abnormal process. This is very important for us to determine what problems exist in the unit system.
Let's talk about the normal frosting situation first. Normal frost formation refers to a relatively uniform and thin layer of frost on the evaporator. It won't frost very thick because the defrosting program had already melted it off before it did. This means that if it frost normally, the surface of the evaporator is a uniform and thin layer of frost. At low ambient temperatures, it won't frost on the supply and return pipelines. There may be a slight nodule in the supply pipeline at the separation head, such as at the capillary tube. The separation head also belongs to the capillary tube, where there may be a slight frost formation, but it will not seriously freeze the entire separation head.
Another type is abnormal frost formation, which is not formed on the evaporator or first on the evaporator. It may be due to the severe freezing of the liquid separation head or the severe freezing of the gas-liquid separator. The compression of the unit used in our current coal to electricity conversion station belongs to the vortex low-pressure chamber return air cooling compressor, which relies on the cold coal return air to cool the motor compressor. If the low-pressure chamber shell of the compressor has already frosted, it is abnormal.
When we arrive at the scene, how can we determine abnormal frost formation? It can be divided into two situations. One is from the throttling device, like an expansion valve, whether it is an electronic expansion valve or a thermal expansion valve, or a capillary tube. From the throttling device out, frost begins to spread all the way to the evaporator, just like a silkworm eating a mulberry, nibbling up the evaporator step by step. The second method is to frost from the return pipe, to the gas-liquid separator, and then to the collection pipe. This is another method of frost formation, also known as reverse frost formation.
There are completely different reasons for the two types of frost formation. First, take the throttle device and frost immediately after coming out of the expansion valve. In this case, from the perspective of liquid supply, if the liquid supply is too low, it will cause the expansion device to frost immediately after coming out. With a reduced flow rate of refrigerant, the cold coal will rapidly absorb heat from the expansion device and expand rapidly. The temperature on the outer surface of the copper pipe is very low, resulting in frost formation on the copper pipe.
After it freezes, the frost layer itself has insulation performance, and the frost layer will be insulated. After insulation, the external environment cannot absorb heat, and the expansion point of the refrigerant will shift back. The outer wall of the copper pipe without frost will continue to absorb heat, and frost will continue to form. This cycle will gradually erode the evaporator. If the expansion valve is too small for the lack of refrigerant, it will form frost like this. For example, as I mentioned earlier, frost starts to form as soon as the expansion valve comes out. However, from a general perspective, the insufficient supply of liquid in this system leads to frost. What is the reason for the insufficient supply of liquid? There are many reasons, such as refrigerant leakage or small refrigerant volume itself, small opening of the expansion valve, ice blockage of the expansion valve, or blockage of the pipeline. Gradually analyze, and in summary, the insufficient supply of liquid leads to this situation.
Frosting starts from the return pipe of the compressor. At this time, the supply volume is too large because the refrigerant of the liquid can hardly absorb heat after passing, absorbing the heat from the pipe wall and evaporating. The temperature of the pipe wall drops very low, and frost will appear on the pipe wall. As the heat pump market watermark forms an insulation layer after frosting, it cannot absorb heat. The frosting point gradually moves back from the compressor return port, and then reverses back, which is caused by excessive liquid supply. What is the reason for the excessive liquid supply? There are many reasons, and it is necessary for everyone to have a certain understanding of the refrigerant system. For example, if the refrigerant is added too much, the expansion valve is opened too large, and the expansion valve cannot be adjusted, it is easier to narrow the scope of frost formation from the perspective of high or low liquid supply.
Next, a very typical problem is the hydraulic shock of the compressor. This is also a very typical case encountered in Beijing's coal to electricity after-sales service. What is a compressor surge? When the compressor is rotating at high speed, whether it is a piston type, a rolling rotor type, or a vortex type compressor, it can only compress gas, not liquid.
Why can compressors only compress gas? Because in daily life, you can also imagine this. For example, it is clearer that in a syringe, when we empty the gas from the suction tube and block the front end, we can still push the piston. If you plug the front end of the syringe with water and then push the piston at the back, you won't be able to move it, then it means that the compressibility of the liquid is very poor. On the contrary, gases have strong compressibility.
Friends who understand car repair better understand that under normal circumstances, atomized gasoline is injected into the cylinder. If the car is running at high speed, the cylinder is compressed at high speed, and suddenly a jet of liquid gasoline is sprayed, there is a possibility of cylinder jacking. The same goes for compressors. What we call liquid hammer is the sudden entry of liquid into the compressor, which has poor compressibility and causes damage to the compressor's vortex plate. This is called liquid hammer.
Last year, I encountered a relatively serious phenomenon of liquid hammer, which is a compressor with increased enthalpy through jet injection. The compressor has an economizer and a small plate heat exchanger, without insulation cotton wrapped outside. The enthalpy increasing circuit throttling device used is a capillary tube with an electromagnetic valve. The electromagnetic valve is not controlled by a circuit board, but is directly connected to the AC contactor of the compressor. That is to say, whether it is refrigeration, heating, or defrosting, in any case, as long as the compressor rotates, enthalpy increasing begins. In this case, the compressor liquid shock is very serious.
Why is liquid hammer very serious in this situation? Firstly, during the normal operation of the compressor, the refrigerant inside the economizer is hot, and we can touch it with our hands. If the system stops and the temperature outside is very low in winter, the warm refrigerant inside the economizer will exchange heat with the outside and condense into a liquid, which will be stored in the enthalpy increasing pipeline. The next time the compressor starts, the enthalpy increasing valve will immediately open, and the refrigerant in the main circuit will not have time to preheat and evaporate the refrigerant in the auxiliary circuit, The liquid refrigerant in the auxiliary circuit is directly sucked into the compressor and sprayed into the middle chamber for compression, so this is inevitably a liquid hammer.
Next, let's talk about the issue of electronic control, mainly based on case studies. Once I received a phone call from a common person, saying that their machines always report low voltage faults, and there is no regular pattern of low voltage faults. Sometimes the machines will report low voltage as soon as they turn on, and sometimes the machines will report low voltage as soon as they close. The compressor will not run, and there is no regular pattern to find. He said that sometimes the machine doesn't even start, and when the power is turned on, the low voltage is reported. Based on his statement, I can determine that it must be a problem with the electronic control system. After I went there, the compressor was able to run. When it started running, I looked at the low-pressure gauge. Generally speaking, the low-pressure gauge would report low pressure at a few tenths of a kilogram, and when the low-pressure gauge dropped to 3 kilograms, it would report low pressure. The low-pressure switch cannot report low pressure at a pressure of 3 kilograms, which indicates that it has nothing to do with the low-pressure switch itself and the system.
After eliminating the issue with the low-voltage switch and the system itself, I mainly investigate the electrical control issue to see if there is a faulty connection in the wiring and if the low-voltage switch is not faulty. I will continue to investigate further. Finally, I found a component on the circuit board called an optocoupler, which plays a role in isolating the switching input. There is a faulty soldering at the corner of the optocoupler plug-in of the electronic control board. After the faulty soldering, its contact is poor, and it will not work well with vibration, resulting in irregular low voltage reporting. When the contact is poor, the signal cannot come in, otherwise it will come in.
After I found out the reason, I did not undergo any major surgery. Instead, I took an electric soldering iron and solder wire and used them to weld and reinforce the solder joint. This problem was completely resolved, and the total repair time was less than 15 minutes. So sometimes after-sales service doesn't mean that major surgery is necessary as soon as you go.
So another typical example is the issue of electronic control anti-interference. The issue of anti-interference is that there is a communication line between the motherboard and the panel. This communication line is usually 485 communication, some manufacturers use 485 communication, and some manufacturers use TTL communication. Regardless of which type, the anti-interference part should pay attention to the separation of strong and weak currents.
Last year, I saw many heat pump installations where workers connected the communication line between the motherboard and the panel to the water pump line. The water pump line had a strong current of 220V, while the communication line had a weak current of 12V. Connecting this communication line to the water pump line caused mutual interference and communication failure.
Let me share another issue with the unit tripping. Last year, some people reported that the air source heat pump was running and tripped, but I don't know why. Once we encounter a tripping problem, we focus on analyzing whether it is caused by a short circuit or overcurrent, an air switch or a leakage protector. There are only three reasons and no other reasons.
What should we do in this situation? After we arrived at the site, we unplugged all the output lines on the circuit board, including the water pump, fan, four-way valve, enthalpy valve, and all other output lines. After unplugging, insert one by one upwards according to the starting sequence of the machine. For example, insert the water pump first to see if it will trip. If it does not trip, it is not related to the water pump. Then insert the fan to see if it will trip. If it does not follow the fan, it is not related. Until we find that there is a tripping phenomenon with a certain component output, then it is a problem with a certain component.
There is also a problem with compressor thermal protection in terms of electrical control, which is also caused by electrical reasons. What is the reason? There is a built-in thermal protection device inside the compressor. When the compressor is heated, its internal switch will jump open. As long as the circuit is cut off, the compressor will no longer work. It has this self-protection mechanism.
Last year, we encountered this problem. A manufacturer's compressor unit did not use a current transformer for circuit protection, but instead used a thermal relay. There is a thermal relay hanging on the AC contactor, which has several characteristics. Firstly, there will be a delay when the thermal relay disconnects. If the current exceeds the load, it will gradually heat up. After heating to a certain extent, it will trip, but due to the delay, the protection is not very timely. There is a cross screwdriver on top of another thermal relay that can be turned to adjust the breaking current. The value it sets is inaccurate and has a very large deviation. For example, if it was originally set to 30 amperes, it could be a 32 ampere break.
So last year, the compressor had this problem. The compressor burned out. What happened? The thermal relay couldn't protect the compressor, and the voltage was often unstable in rural areas of Beijing. Electricity is not always low, it continues to be low. If the voltage continues to be low, the machine cannot start, and the voltage when the unit starts is not less than 220 volts, sometimes even 230 volts. After the unit has been running for a period of time, the voltage suddenly drops, only for two or three minutes.
After reporting the fault, we went and took a clamp current meter to measure it. The voltage was not low again, around 225 volts or 227 volts. When the unit starts, it is not low. When the compressor runs and the voltage suddenly drops, the current will increase because the compressor is a loaded motor. The voltage has decreased and the current has increased. At this point, the compressor will generate heat, and the heating capacity of the compressor coil is greater than the original heating capacity. Therefore, the incoming refrigerant is fixed because its coil is cooled by refrigerant return air. The amount of refrigerant coming over is fixed, and the compressor coil generates a large amount of heat. If the refrigerant cannot cool the compressor coil, there will be two situations: one is to report a high exhaust temperature, and the other is to protect the compressor itself when it heats up.
The common people don't understand because there is no current transformer used, and the control panel does not report any faults, but instead shows that everything is normal, but the compressor does not run. At this point, the common people argue with us that the machine is broken. We were also in a difficult situation and couldn't explain it clearly to them, so we had to ask the manufacturer to add current transformers to it. The detection ability of current transformers is very accurate, and the breaking ability is also very fast. If the compressor is cut off in one or two seconds after exceeding the current in the program, it can completely achieve this without overheating the compressor. At the same time, I will also report a fault code on my dashboard, telling the people that the overcurrent and overload of the compressor are caused by low voltage. At the very least, the responsibility is clearly divided.
In a nutshell, let's talk about the drainage system. Let's talk about some of the problems we encountered last year: mainly because people are unwilling to invest in renovating the terminal, most of them use radiators. Can the combination of radiators and air sources achieve heating effects， Beijing, because the government has provided insulation for people's houses, strictly speaking, can achieve this. The heat dissipation is not the main issue, it is mainly due to dirt and blockage.
Last year, I encountered a lot of rust on the radiator and added a Y-shaped filter, but I still blocked the plate heat exchanger. After being blocked, the water flow decreases, causing a natural high pressure and various chaotic problems.
On the other hand, the quality of the water pump itself is not good, and the selection of the heat pump is too small, resulting in a flow rate that cannot be reached, and there are also cases where high pressure is reported. In the end, the customer caused it by themselves, such as using floor heating at home, closing all the unused rooms on their own, and then opening one of their own rooms. The water flow naturally cannot reach, and then the high pressure is reported. Finally, the head of the water pump caused an accident in the entire system. The end of the radiator and fan duct close to the machine is hot, while the end of the duct far from the machine is cold. Because water cannot pass through, we can only adjust the valve manually, but this problem has not been fundamentally solved. This is a problem where the pump head cannot be reached.
Finally, let me share with you an experience. In the end system, fan coil units and radiators must not be mixed. The end is either all radiators or all fan coil units. If a fan coil unit is added to the radiator, the fan coil unit will never heat up because its system resistance is different. Hot water is taken as a shortcut, and even radiators with low resistance pass through. The fan coil unit cannot pass through hot water, This is a typical water system problem encountered last year.