Analysis and troubleshooting of common faults in cold and hot water air conditioning systems

Analysis and troubleshooting of common faults in cold and hot water air conditioning systems

Common faults of cold and hot water air conditioning systems mainly come from three major parts: the refrigeration system, the water pipe system and the surrounding environment. Regardless of which part of the cause of the failure, it will eventually show up in two phenomena: cold and heat source equipment failure alarms and shutdowns or the air conditioning effect deteriorates.

Analysis and troubleshooting of common faults in cold and hot water air conditioning systems

   Most of the products produced by the manufacturers use the microcomputer main control panel to intelligently control the equipment and system, and have the functions of fault alarm and display fault code. However, the control mechanism and setting parameters of the main control board of each manufacturer and the meaning of the display code are different. Only some common problems can be analyzed here. For specific failure analysis and troubleshooting methods, please refer to the maintenance manual provided by each manufacturer. related information.

Analysis and troubleshooting of common faults in cold and hot water air conditioning systems

  The alarm and safety protection measures commonly used by various manufacturers include the following aspects:

   1. The high and low pressure protection is realized by the high and low pressure controllers. Once an alarm is issued, all the relays on the relevant circuit will be powered off and the corresponding alarm indication appears. Once the system returns to normal, the low-pressure pressure controller can automatically reset, and the high-pressure pressure controller generally resets automatically.

  2. The low water flow protection is realized by the water flow and water pressure difference switches installed in parallel on the waterway. If the water flow is lower than the top set value, the unit will stop running and the corresponding alarm indication appears.

   3. Power failure protection When the power supply is restored after a power failure, the unit will automatically return to the state before the power failure. The compressor delayed start timer and defrost timer will restart. Generally, a sudden power failure will not change the original parameter settings.

  4. The antifreeze protection is realized by the sensor installed on the water outlet of the plate heat exchanger. When a failure occurs, the corresponding alarm indication appears and the compressor stops and works. After returning to normal, the system automatically returns to its original state.

  Common failure analysis and troubleshooting methods of refrigeration system

   1. The refrigeration unit cannot start working

cause of issue:

  A. Whether the main circuit power is on.

  B. Is the circuit voltage normal?

  C. Whether the contact of the pressure controller is closed.

  D, the temperature controller contact jumps out.

  E, the winding of the compressor motor is burnt or short circuit between turns. elimination method:

  A. Generally, a multimeter can be used to test whether the main circuit has voltage, or an electric pen can be used to test whether the circuit has power.

  B. When the circuit voltage is significantly lower than the rated value, the compressor motor will not be easy to start and make a humming sound. After measuring the voltage with a multimeter, the voltage value should be stabilized, otherwise it will burn out the electric power and not the winding.

  C. Check whether the contact of the pressure controller is closed. Use a multimeter to test. If the contact brick is in the normally open state, the pressure controller should be adjusted and tested.

  D. Rotate the thermostat adjustment lever to the low temperature area to see if the contacts are closed. If it is not closed, remove the temperature sensing bag and immerse it in warm water, and then see if the contact is moving (closed). If it does not work, in most cases the second is the leakage of the temperature sensing medium in the temperature sensing bag, and the temperature controller needs to be removed for repair or replacement.

  E. If the power is turned on, it will cause the fuse to blow or the circuit breaker to trip, and other electrical appliances and circuits are not faulty. In most cases, the motor windings are burned or inter-turn short-circuits. Use a multimeter to check whether there is a short circuit between the terminals and the shell, and measure the resistance of each phase. If it is a short circuit or a phase resistance is small, it means that the winding turns are short-circuited or the insulation is burned. The power cord on the motor terminal should be removed during testing. If the fish cannot be caught with a multimeter, the insulation resistance can be measured with an insulation resistance meter. If its resistance is equal to zero, it means that the insulating layer has been broken down. If the winding is burnt or short circuit between turns, rewind the coil or replace the compressor.

  2, the refrigeration unit suddenly stops during operation

cause of issue:

  A. Sudden shutdown caused by low suction pressure

  B. Sudden shutdown caused by excessive exhaust pressure

  C, sudden shutdown caused by low oil pressure

  D. Sudden shutdown caused by motor overload.

elimination method:

a. Temporarily close or short-circuit the contact of the low-pressure pressure controller, then start the compressor, and check the indicated value of the suction pressure gauge. If it is indeed lower than the set value of the pressure controller, the system should be checked during operation an examination. The low suction pressure is mainly caused by a blockage in a certain part of the system or insufficient refrigerant, so these faults should be eliminated according to the relevant operating procedures.

  B. Excessive exhaust pressure is mainly caused by insufficient cooling air volume, condenser fouling, air in the system, excessive refrigerant charging, and poor exhaust pipe and condenser pipe. The reasons should be found out item by item, and these failures should be eliminated.

c. If the lubrication system fails and the oil delivery pressure is lower than the adjustment position, the oil pressure difference controller will act and cut off the power supply, causing the compressor to stop suddenly. At this time, the lubrication system should be checked and restarted after the fault is removed. compressor. If there is no oil pressure difference controller protection device, always check the oil pressure and bearing temperature rise. If the oil pressure is too low and not detected in time, the bearing will "bite", and the motor will be overloaded with a "humming" sound. Therefore, for small and medium-sized compressors without oil pressure difference controller, always check the working condition of the lubricating oil pump system.

  D. When the indoor thermal load exceeds the cooling capacity of the unit, or the power supply voltage drops, the thermal relay will trip, or the fuse will blow, and the motor will stop.

  3, the refrigeration unit has insufficient cooling capacity

cause of issue:

  A, the sealing performance of the room becomes worse

  B. Compressor efficiency becomes worse

  C, filter clogged

  D, there is air in the system

  E, too much refrigerant charge

  F, insufficient refrigerant

  G, the expansion valve flow is the largest

  H, the expansion valve flow is too small or the valve inlet filter is not unblocked.

  I. There is refrigerating oil in the evaporator.

elimination method:

  A. Check whether the doors and windows of the room are tightly closed. Otherwise, the cooling capacity will be severely depleted and the room temperature will not drop.

  B. Most of the reasons for the deterioration of the efficiency of the compressor are due to the considerable wear of the moving parts, the increase of the matching clearance, or the decrease of the air valve sealing performance, which causes the increase of air leakage. The compressor efficiency has deteriorated and needs to be disassembled and repaired. If it cannot be repaired, replace the compressor with a new one.

c. Most of the meshes on the filter screen are blocked. When the refrigerant passes through the filter, the resistance is very large, and the flow z* is reduced, resulting in insufficient cooling capacity of the refrigerator. If the filter is blocked, remove the dirt, or replace with a new one. The filter is then installed back into the system.

  D. When the system contains a small amount of air, it will cause the suction and exhaust pressure to rise, and the cooling capacity is insufficient. At this time, the air should be discharged from the bypass hole of the compressor discharge shut-off valve, or the refrigerant in the system should be discharged, leak detection, vacuuming, and refrigerant filling should be performed again.

  E. Excessive refrigerant injection will cause high suction and discharge pressures, lower cooling capacity, and difficulty in lowering the room temperature. At this time, the excess refrigerant must be discharged from the system.

  F. The amount of refrigerant circulating in the system is insufficient, resulting in insufficient cooling capacity. The phenomenon of insufficient refrigerant amount is that the suction and discharge pressures are low, but the discharge temperature is high, and intermittent "squeak" airflow sounds can be heard at the expansion valve, and the sound is louder than usual. If the expansion valve hole is enlarged, The suction pressure still does not rise, and the equilibrium pressure of the system after shutdown may be lower than the saturation pressure corresponding to the ambient temperature. Insufficient refrigerant is obviously caused by leakage points in the system. Therefore, you should not rush to add refrigerant and find out the leakage points first, repair them, and then add refrigerant.

g. The flow rate of the expansion valve is compatible with the refrigeration capacity at the evaporating temperature required by the refrigeration unit: if the working conditions of the refrigeration system change due to some reasons in the system, such as the decrease of the compressor's displacement and the condensation temperature The high temperature, the change of the refrigerant charge in the system, etc. will cause the flow rate of the expansion valve to exceed the automatic adjustment range, and then it must be re-adjusted. When adjusting the expansion valve, rotate the valve stem 1/4 to 1/2 turn each time and run for about 20 minutes to observe the change of suction pressure. If the suction pressure still has no change or the change is not significant, adjust the valve stem again.

  H. If the expansion valve hole is adjusted too small, the refrigerant flow will decrease, the evaporation pressure will be low, and the refrigeration unit will have insufficient cooling capacity. The valve hole should be adjusted appropriately. The reason why the expansion valve hole is too small may be that it was not adjusted during debugging, or it may be that the valve inlet filter is a bit blocked, causing the valve hole flow to decrease. After the expansion valve hole is adjusted, if the suction pressure does not rise, It is possible that most of the inlet filter of the expansion valve is blocked by dirt and is not unblocked. When the filter screen is blocked, the entire valve body will be frosted; if the valve hole is too small, only the half of the valve body will be frosted. The filter should be removed for cleaning if it is not smooth.

  T, some refrigerants and refrigerating machine oil can dissolve each other. Therefore, when the refrigerant in the system circulates, it is inevitable that there will be refrigerating machine oil remaining in each component. Therefore, the oil must be drained to remove the refrigerating oil in the evaporator, and it must be removed, purged and dried.

  4, the refrigeration unit has no air-conditioning

cause of issue:

  A. The temperature-sensing agent in the temperature-sensitive bag of the expansion valve leaks.

  B, the expansion valve is blocked.

  C, the filter is clogged.

  D. Almost all refrigerant in the system leaks.

  E, the compressor suction and discharge valve pieces are broken.

elimination method:

a. The failure phenomenon is that the suction pressure is very low and the expansion valve is not frosted. At this time, the expansion valve should be removed for inspection, unscrew the expansion valve inlet buckle, and take out the filter to see if there is any clogged dirt. If the filter screen is not blocked, you can unscrew the outlet connector of the expansion valve and blow or inhale against the outlet connector with your mouth. If you cannot blow or inhale, the valve needle is closed. Generally speaking, this can only be the result of the leakage of the temperature sensing agent in the temperature sensing bag. Leakage of temperature sensing bulb is generally not easy to repair, only replace the entire expansion valve.

  B. The abnormal phenomenon of valve hole clogging is that the suction pressure is very low and the valve is not frosted and there is no sound of air flow. In this case, it is generally to take a case-by-case inspection and analysis, and to eliminate doubts one by one. If the expansion valve body is heated first to check whether the ice plug or the lubricating oil is frozen and blocked, if the heating is invalid, then a doubt is eliminated. Then tap the side of the inlet of the valve body with a wrench to check if the filter is clogged. If it is still ineffective, the remaining w* may be the leakage of the temperature sensor. Generally, it is heated or tapped first, and then removed when it is invalid. The expansion valve is thoroughly inspected.

  C. The phenomenon that the filter is blocked by dirt is also a vacuum in the low pressure section, and the exhaust pressure is low. The filter housing can be hit with the wrench handle. After that, if the suction pressure can be increased, it indicates that the filter is indeed blocked. To make the filter unblocked, it is necessary to remove the filter, clean the filter, dry it and install it again, re-evacuate and fill with refrigerant.

  D. The phenomenon after almost all refrigerant leaks is that the suction pressure is vacuum, the exhaust pressure is extremely low, and the exhaust pipe is not hot. Before refilling the refrigerant, the refrigeration unit should be pressure-checked and leaked, and then vacuumed and filled with refrigerant.

  E. If the suction valve plate is broken, high-pressure steam will flow back and forth between the cylinder and the suction chamber; if the exhaust valve plate is broken, high-pressure gas will flow back and forth between the cylinder and the exhaust chamber. It can be seen that no matter which kind of valve is broken, the refrigerant cannot be discharged from the compressor, and the refrigeration system cannot refrigerate. When the suction valve plate is broken, the suction pressure gauge pointer swings very sharply, the suction pressure is high, and the suction temperature is also high; when the exhaust valve plate is broken, the exhaust pressure gauge pointer swings very sharply. Exhaust pressure is very high, cylinder and cylinder head are very hot. When you find this phenomenon and judge the fault, you should stop the machine in time, drain the refrigerant in the system, sweep the cylinder head, check the valve and repair it.

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