For refrigeration system maintenance and engineering technicians, the electronic expansion valve failure will lead to commercial freezers, cold storage and other equipment refrigeration efficiency plummet or even downtime, resulting in economic losses. Mastering the common types of failure and scientific diagnosis method is the key to shorten the downtime and quickly repair the equipment.
Electronic expansion valve (EEV) as the core temperature control element of the refrigeration system, compared with the traditional thermal expansion valve (TEV), through the electronic controller to accurately regulate the refrigerant flow, significantly improve the system’s operating efficiency and stability.
What is Electronic Expansion Valve?
Electronic expansion valves are widely used in commercial freezers, walk-in coolers and other types of refrigeration systems, the core role is to accurately control the flow of refrigerant into the evaporator.
It is an upgraded version of the traditional thermal expansion valve — the traditional thermal expansion valve relies on mechanical structure (spring, bellows, push rod) to control the amount of refrigerant release, to maintain the evaporator superheat stability; while the electronic expansion valve with the help of an electronic controller to receive signals, regulate the degree of openness, the precision of temperature control and the efficiency of the system are better.
How Does an Electronic Expansion Valve Work?
The workflow of the electronic expansion valve is centered around “detection – processing – control – feedback” to form a closed loop, ensuring that the refrigerant flow is always adapted to the system requirements:
- Intelligent perception layer data acquisition: the system is equipped with high-precision temperature, pressure and flow sensors, which capture operating parameters in real time with millisecond sampling frequency and build a full-dimensional working condition data pool to provide the core basis for fault diagnosis.
- Algorithm Analysis and Parameter Calculation: The control unit digs into the sensor data through the built-in intelligent algorithm, and accurately deduces the required refrigerant flow parameters in the target temperature zone by combining with the thermodynamic model.
- Electrical signal command drive: Based on the calculation results, the control unit sends pulse width modulation (PWM) electrical signals to the electronic expansion valve actuator, realizing the digital adjustment of the valve opening degree.
- Dynamic flow precision regulation: The electronic expansion valve adjusts the refrigerant flow in real time by virtue of the electromagnetic drive mechanism with high response speed to ensure that the heat exchange efficiency of the evaporator is always maintained in the optimal state and to guarantee the stability of the system operation.
- Closed-loop feedback optimization mechanism: the sensor continues to return real-time operating data, the control unit through the PID control algorithm to dynamically correct the valve opening, in order to enhance the cooling performance of the system at the same time, to achieve continuous optimization of the energy efficiency ratio.
What Are The Common Faults of Expansion Valves?
Electronic Expansion Valve failures are mostly related to mechanical stall, electrical abnormalities, improper installation, and the impact of different failures on the system varies, and can be divided into the following 7 categories:
Electronic Expansion Valve Jammed
This type of failure is mostly a “loss-type problem” after a long period of operation. Deposits of impurities in the piping, buildup of metal oxides, or failure of lubrication inside the valve can prevent the needle from moving properly. Once jammed, the valve will be fixed at a certain opening degree, losing the ability to regulate, the system can not adjust the refrigerant flow according to the load changes, light refrigeration efficiency decline, heavy evaporator frost or compressor overload.
Electronic Expansion Valve Coil Dislodged
The coil of the electronic expansion valve, as the core power component, is vital to be installed securely. Negligent fixing during installation, constant vibration during operation, and improper operation during maintenance can cause the coil to detach from the valve body during the entire life cycle of the equipment. Once the coil is detached, the electronic expansion valve will lose its regulating function completely due to the loss of the driving source, which will lead to the interruption of the operation of the entire refrigeration system.
Damage to The Coil of EEV
When the voltage exceeds the rated range, it will directly penetrate the coil insulation; if the humidity of the working environment exceeds the standard, water vapor intrusion into the interior will lead to short circuit.
In addition, with the increase of the use of years, the coil insulation layer will gradually deteriorate, which will ultimately lead to circuit breakage. Once the coil is damaged, its electromagnetic function will be invalid, unable to generate the electromagnetic torque to drive the valve needle, resulting in the loss of precise adjustment of the valve.
Electronic Expansion Valve Wiring Loose
Wiring faults are like “invisible killers” lurking in the system, seemingly subtle but hidden hidden danger. Common types of failure include: false connections in plugs due to negligent assembly, oxidized layers in terminals due to environmental erosion, and internal breaks in wires due to mechanical stress (constant vibration, external drag).
These problems can directly cut off the signal transmission channel between the control unit and the electronic expansion valve, causing the valve to lose control because it does not receive regulation commands, and ultimately leading to refrigeration system operation disorders.
Electronic Expansion Valve Coil Installation Is not in Place
In the process of assembling the electronic expansion valve, if the coil is not tightly embedded with the valve body, residual assembly gaps will damage the integrity of the magnetic circuit.
After the damage to the magnetic circuit, the coil drive efficiency will be significantly reduced, resulting in a slight delay in the response of the valve regulation, affecting the sensitivity of the system temperature control; the heavier directly lead to the valve needle can not be driven normally, resulting in the failure of the system temperature control.
Electronic Expansion Valve Body Cracks and Leaks
Valve body cracks and leaks are often triggered by material defects and external factors together. Manufacturing process, if the valve body there are air holes, sand holes and other process defects, or the choice of material strength is not up to standard, has buried a hidden danger; and in the installation process, if the operation is not appropriate resulting in excessive concentration of mechanical stress, will also destroy the valve structure.
In addition, when the equipment is in a low-temperature environment, if there is a lack of effective protective measures, the valve body refrigerant freezing expansion, very easy to cause frost cracking accident. Once this type of failure occurs, the refrigerant will continue to leak from the cracks, and due to the damage is usually difficult to repair, generally need to replace the valve body as a whole.
EEV Valve Body Welding Leakage
Welding process problems is the main cause of such failures: welding temperature control is not appropriate, false welding, or welds there are sand holes, as well as later due to temperature changes in the thermal stress cracking, will lead to refrigerant from the weld leakage slowly.
Initial leakage is small, not easy to detect, often need to be detected through the pressure leakage detection, long-term leakage will lead to insufficient cooling capacity of the system, may also damage the compressor.
Scientific Diagnosis of Electronic Expansion Valve Failure
To diagnose the electronic expansion valve failure, can not be blindly disassembled, it is recommended to follow the “first external and then internal, first electrical and then mechanical” principle, step by step investigation, accurate positioning of the problem.
Diagnosis of The Core Principles
Fault diagnosis pay attention to the logic and efficiency, modify the optimization of the expression of the professional terminology, presented in points to make the organization clearer.
- Appearance pre-screening: first check the coil connection of the electronic expansion valve to see if there is any shedding or loosening, and at the same time, carefully check whether the terminals are tight to ensure that there is no hidden danger of poor contact.
- Internal fine inspection: After the completion of the appearance inspection, the valve body running state for in-depth testing, focusing on checking whether there is a spool jammed, valve seat wear and other abnormalities, in order to timely discover the potential internal faults.
- Electrical inspection: carry out a comprehensive inspection of the electrical system of the electronic expansion valve, covering coil performance testing, power supply stability verification and signal transmission integrity verification, to ensure the normal operation of the electrical part.
- Mechanical inspection: After confirming that the electrical system is trouble-free, further inspect the mechanical structure, focusing on the smoothness of the valve needle and the integrity of the valve body, and accurately locate the mechanical trouble spots through detailed inspection of key parts such as transmission parts and sealing components.
Through this systematic inspection process from the surface to the inside, first electrical and then mechanical, we can effectively avoid diagnostic omissions and significantly improve the overhaul efficiency.
Hearing and Tactile Preliminary Inspection
When the power is on and running, close to the electronic expansion valve body, listen carefully to whether there is a “click, click” step sound, which is the normal sound of the coil driving the valve needle action; at the same time, touch the valve body with your hand to feel whether there is a slight vibration. If there is no sound or vibration, the probability is that the coil is not working or drive failure.
Confirm whether The Installation Status Is Compliant
Improper installation is the root cause of many failures, you need to focus on checking three points:
- Coil installation in place check: installation of electronic expansion valve coil, should be in accordance with the specifications of the operation, aligned with the valve body mounting port slowly downward pressure, hear the “click” sound that is indicated to set into the slot and lock tight.
After installation, pull gently to confirm that there is no loosening, and at the same time, use a flashlight to check the side illumination, if the gap between the coil and the valve body is more than 0.5 mm, it is necessary to re-install to prevent abnormal electromagnetic induction or refrigerant leakage.
- Connector solidity test: using a combination of visual and manual shaking, check the electronic expansion valve coil plug and the main board interface connection, make sure that the plug is completely inserted into the interface slot, no loose, skewed and poor contact phenomenon, if necessary, you can use a multimeter to detect the connection resistance value is normal.
- Wiring polarity verification: use a multimeter to check the polarity of the power supply before wiring to ensure that the input voltage matches the rated parameters of the coil. According to the wiring diagram of the equipment, check the positive and negative polarity (red positive and blue negative) through the color coding, and double wrap the exposed end with insulating tape.
After wiring, use the equipment self-test to simulate power on and off, monitor the coil current fluctuation (not exceeding the rated value ±5%) and the valve body action time (within 0.5-1 seconds), abnormalities in the immediate power-off troubleshooting, to avoid coil burnout or valve body stagnation.
Electrical Test (voltage + resistance)
Electrical parameters are the key to determine whether the coil and power supply is normal, need to use a multimeter test:
- Voltage test: use a multimeter to measure the voltage at the input of the electronic expansion valve coil, the normal operating voltage range should be DC 12V ± 1.2 V. If the measured voltage exceeds this range, it is necessary to further investigate the stability of the output of the power supply module and whether there is a voltage drop in the line connection.
- Resistance test: In the power-off state of the equipment, measure the resistance value between the winding of each phase and the common terminal (usually identified as blue or gray wire). The standard resistance value should be 46Ω ± 3Ω, if the measured value deviates from the interval, there may be winding faults.
If the resistance value is infinite, indicating that the coil is disconnected; if the resistance is small or zero, indicating that the coil is short-circuited; if the resistance is normal, but the valve does not move, it can be judged to be the valve body jammed.
Targeted Diagnosis of Specific Faults
There are more precise diagnostic techniques for different fault types:
- Coil off: electronic expansion valve coil off common faults, mostly caused by equipment vibration, installation is not secure. When troubleshooting, you can visually check the installation status of the coil and the valve body.
If the coil is found to have slipped off, it needs to be re-installed accurately to avoid tilting and loosening. After installation, start the system test, if it returns to normal, it can be basically determined that this fault, the follow-up also need to continue to observe the system operation.
- Damaged coil: Use resistance test method to detect the coil. Use professional instruments to measure the resistance, and the standard value of 46Ω ± 3Ω compared to the resistance value over the range or open-circuit state that indicates that the coil is damaged, and need to be replaced in a timely manner.
Different brands and models of electronic expansion valve coil resistance standards are different, testing should refer to the product manual technical parameters to ensure accurate results.
- Loose wiring: Loose wiring will cause the electronic expansion valve to be unable to receive control signals. When checking, first confirm whether the wire harness plug is tightened in place; gently shake the connection part to observe whether there is any intermittent fault in the system.
Finally, use a multimeter to detect the wiring with the through-break gear, if it shows “not available”, then troubleshoot the loose plug pins or internal breakage of the wires and other problems, and repair or replace the damaged wiring in a timely manner.
- Inadequate coil installation: Inadequate coil installation will affect the electromagnetic performance, resulting in abnormal valve control. When checking the bottom of the coil and the top of the valve body to observe the fit, if there is a gap or tilt, should be disassembled and reinstalled. A level can be used to assist in calibration to ensure a tight fit and correct orientation. Re-check and perform a system test after installation to ensure proper operation.
Preventive Maintenance Tips for Electronic Expansion Valve
Instead of repairing after failure, it is better to do maintenance in advance to prolong the service life of the electronic expansion valve and reduce the probability of failure:
Deeply Clean The Piping System before Installation
Welding slag, oxidized skin, moisture, and other impurities left in the piping of the refrigeration system will enter the electronic expansion valve with the refrigerant cycle, causing spool blockage or corrosion of the internal structure.
Before installation, the pipeline should be purged with high-pressure nitrogen, focusing on cleaning up the welding parts, until no impurities remain in the blown gas, to ensure that the cleanliness of the pipeline is in line with the system operation requirements.
Strengthen Protection of Valve Body
When welding, high temperature is easy to cause irreversible damage to the internal precision components of the electronic expansion valve. It is recommended to use wet cloth to wrap the valve body and use cooling device to monitor the temperature in real time to control the surface temperature of the valve body below 60℃.
Strictly follow the welding process parameters to control the welding temperature at 420-450℃, and the welding time of a single weld is no more than 3 seconds, so as to avoid quality hazards such as false weld and sand holes.
Special Maintenance Mechanism for Old Units
For refrigeration units running for more than 3 years, it is recommended to establish annual deep maintenance system. Focus on circulating cleaning and vacuum drying of the system, and synchronize the replacement of drying filter and liquid storage tank to ensure the purity of refrigerant, and effectively prevent the valve stagnation failure caused by the accumulation of impurities.
Optimize The Equipment Operation and Management Strategy
Frequent starting and stopping will make the electronic expansion valve coil undergo violent current impact and accelerate the aging of the insulation layer. It is recommended to set the shortest start-stop interval (≥5 minutes) and optimize the operation curve with intelligent control system in daily operation to keep the equipment running stably and reduce the risk of coil failure due to current impact.
Conclusion
Electronic expansion valve is the core component of refrigeration system, and its performance is related to the energy efficiency and life of the equipment.
For maintenance personnel and enterprises, it is of great significance to master fault diagnosis and prevention methods. Troubleshooting can be based on the steps in this article, the complexity of the problem to seek timely help from professional service providers, it is recommended to immediately carry out a preliminary inspection of the equipment.
