Trouble and maintenance of electronic expansion valve and four-way valve

Last Updated on November 12, 2021 by Shawn Lee

Among central air conditioners, the most commonly used ones are electronic expansion valve and four-way valve. The electronic expansion valve has the function of throttling and reducing pressure. The four-way valve changes the functions of two air conditioners by changing the flow direction of refrigerant in the system, and realizes the switching of cooling, heating or defrosting functions. These two parts are very important to air conditioning.

Four-way valve

Four-way valve, also called electromagnetic four-way reversing valve, is an important component of air conditioning system, which mainly plays the role of cooling and heating switching.

Diagnosis method of cross-talk-“touch”: whether in cooling or heating mode, cross-talk means that the cold suction pipe is not cold and the hot exhaust pipe is not hot. The temperature difference between air intake (5~15℃ in rated cooling mode) and air exhaust (60~90℃ in rated cooling mode) can be measured by temperature measuring instrument. If the error does not obviously indicate that the four-way valve is cross-connected, if there is no temperature measuring instrument, it can be judged by hand “touching”.

Diagnostic method of sticking-“Listen”: When working, turn the coil gently, and listen to whether there is “squeaking” electromagnetic noise, which indicates that there is basically no problem with the electromagnetic coil. If there is no obvious reversing sucking sound during reversing, it indicates that the four-way valve may be stuck. You can tap it gently with a small wooden stick to see if it can recover.

Coil diagnosis method-“measurement”: usually, the supply voltage of the solenoid coil of the four-way valve is AC 220V, so you can measure whether the voltage at both ends of the coil is normal first, and then use a multimeter to determine whether the resistance value of the solenoid coil is normal.

Trouble causes and solutions:

The system contains impurities such as welding slag, which blocks the slider of the four-way valve; At this time, the four-way valve should be powered on and off frequently on the premise of starting up. At the same time, the four-way valve should be pounded several times with a wooden hammer to push the slider with refrigerant impulse.

The wrong type of lubricating oil or other chemical substances are added to the system, which corrodes the rubber parts in the four-way valve; At this time, it is necessary to replace the four-way valve, clean the system and replace the lubricating oil.

The four-way valve is stuck, which causes the system to keep high temperature and high pressure, and breaks the slider in the four-way valve; It is necessary to replace the four-way valve and find out the reason why the four-way valve is stuck.

The electronic expansion valve

Electronic expansion valve: it is a throttling element that can enter the refrigerant flow of the refrigeration device according to the preset program. In some cases where the load changes drastically or the operating conditions are wide, the traditional throttling elements (such as capillary tubes and thermal expansion valves, etc.) can no longer meet the requirements of comfort and energy saving. The electronic expansion valve combined with compressor variable capacity technology has been widely used. At present, the research on electronic expansion valve includes three directions: application research, flow characteristics, control strategy and algorithm.

Normal electronic expansion valve: “click” after plugging in. If there is no noise, or the expansion valve starts to frost after the compressor works during refrigeration, check whether its coil and power supply are normal (12V pulse electricity). If the voltage is normal, it means that the computer board is normal. If there is no sound in the expansion valve at this time, it means that the expansion valve is defective. At this time, measure the DC resistance of the coil of the electronic expansion valve first. If it is normal, it may be the internal organs of the valve body blocked, which can be purged with high-pressure gas.

Fault phenomenon 1: the valve of the electronic expansion valve is fully closed

Analysis and maintenance: normally, the needle valve is in the open position before the electronic expansion valve is electrified. When the valve body leaves the factory, the valve opening is 480 pulses. However, because the rotor is fixed by screw structure, the position of the rotor may change due to vibration during transportation, and finally the valve is fully closed. In case of this fault, reset operation can be performed after power-on to ensure that the valve body is in an open state, so that the opening of the needle valve can be controlled by the stepping motor, thereby adjusting the flow rate

Malfunction phenomenon 2: After starting, there is noise in the electronic expansion valve

Analysis and maintenance: if the noise is too high, it indicates that its internal devices are stuck and need to be replaced as a whole to solve it. It is worth mentioning that it is normal if there is a “click” sound in the valve body when the power is turned on. After the air conditioner is powered on, [this article comes from refrigeration encyclopedia WeChat official account], the electronic control board will send the pulse of full opening or full closing to the electronic expansion valve. At this time, when the rotor of the electronic expansion valve turns to the maximum opening, it collides with the limit device and makes a “click” fricative sound. When the air conditioning system is filled with refrigerant, the resistance of rotor rotation increases and the sound propagation mode changes, the action sound of the electronic expansion valve will become very small.

Malfunction phenomenon 3: electronic expansion valve does not operate.

Analysis and maintenance: When the power supply is turned on, listen to whether there is a “click” sound in the valve body. If not, check whether the valve body is completely sleeved with the coil, whether the coil is connected with the circuit board normally, and whether the coil power supply voltage meets the requirements (12 V 1.2 V). If all the above inspections are normal, check whether the valve body can be fully opened. If not, the valve body is broken and needs to be replaced. If the valve body can be fully opened, check whether the pulse number of valve full closing is greater than 480pps; if it is lower than 480pps, check the driving mechanism.

Malfunction phenomenon 4: the electronic expansion valve is stuck

Analysis and maintenance: the fault is caused by impurities entering the electronic expansion valve and accumulating when the refrigerant flows. When the impurities are embedded in the valve body, the friction force of the rotor rotation will increase, causing the phenomenon of seizure, which is usually solved only by overall replacement.

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