1. Basic knowledge
(1) Installation position
The electronic expansion valve is usually installed in the outdoor unit vertically, and its function in the refrigeration system is the same as that of the capillary tube, that is, reducing pressure, throttling and regulating refrigerant flow.
(2) Valve as-electronic expansion
The electronic expansion valve assembly consists of a coil and a valve body. The coil is connected with an outdoor electromechanical control system, and the valve body is connected with a refrigeration system. The coil is clamped on the valve body through a clamp.
(3) Main components
The valve body is mainly composed of rotor, stem and base. Together with the coil, it is called the four parts of electronic expansion valve.
Coil: equivalent to the stator, which converts the output signal of the electric control system into a magnetic field, so as to drive the rotor to rotate.
Rotor: it is composed of permanent magnet and connected with valve rod at the top. When it works, it receives the drive of coil and makes forward or reverse spiral rotation movement.
Stem: fixed on the base by screws in the middle. Driven by the rotor, the rotor drives the stem to move up or down in a straight line.
Base: mainly composed of brass, the upper part is connected with the valve rod, and the lower part leads out two pipes to connect with the refrigeration system.
The auxiliary parts are provided with a stopper and a cylinder iron sheet.
(4) Refrigerant flow
The connecting pipe of the example electronic expansion valve is H-type, and there are two copper pipes connected with the refrigeration system. It is assumed that the vertical pipe directly below is called a pipe, which is connected to the two-way valve; the horizontal pipe is called B pipe, which is connected to the condenser outlet pipe.
Refrigeration mode: as shown in the left figure above, the refrigerant flow direction is B → a. the low-temperature and high-pressure liquid flows out of the condenser and becomes low-temperature and low-pressure liquid after double throttling by capillary tube and electronic expansion valve. It is sent to the evaporator of the indoor unit through the connecting pipe through the two-way valve.
Heating mode: as shown in the right figure above, the flow direction of refrigerant is a → B. the evaporator (at this time, it is equivalent to the outlet of condenser) flows out low-temperature and high-pressure liquid, which is sent to the electronic expansion valve and capillary double throttling through the two-way valve, and becomes low-temperature and low-pressure liquid, which is sent to the outlet of condenser (at this time, it is equivalent to the outlet of evaporator).
2. Measure the coil resistance
According to the number of leads, the coil can be divided into two types: one is 6 leads, two of which are connected to the common terminal power supply DC 12V (blue wire for example), and the other four are connected to the CPU control (black wire, yellow wire, red wire, orange wire).
The method of measuring the coil of the electronic expansion valve is the same as that of measuring the coil of the stepping motor. Use a multimeter to measure the resistance, connect the black probe with the blue wire of the common terminal, and measure four control leads with the red probe. Above, the resistance values of blue and black, blue and yellow, blue and red, blue and orange are all 47 Ω.
The resistance between 4 leads connected to drive control shall be 2 times of the resistance between common end and 4 leads. In the above figure, the measured resistance values of black and yellow, black and red, black and orange, yellow and red, yellow and orange, and red and orange are all 94 Ω.