PCB Blog - Introduction of aircon PCB

The aircon PCB is the control center of the air conditioning system, responsible for controlling the operation of the air conditioning system and ensuring its normal operation.

aircon PCB

Working principle of  aircon PCB

 Aircon PCB refers to an electrical system that uses a circuit controller to achieve functions such as air conditioning refrigeration, heating, dehumidification, and air supply.

1. Power supply part of the electrical system: After connecting the indoor and outdoor power supplies, AC enters the distribution box, and then enters the air conditioning controller through the circuit, which is converted into DC voltage to operate the electrical components.

2. Lines that carry voltage and transmit information: The lines that transmit power and signals include high-voltage and low-voltage lines. High-voltage lines mainly carry 220V voltage, while low-voltage lines transmit control signals and data between the controller and indoor and outdoor mobile mechanisms, such as communication lines, sensor lines, drive lines, etc.

3. Compressor part: The compressor is the core component of the electrical system, which compresses the refrigerant and increases its temperature and pressure, allowing it to release heat and cool in the condenser to achieve refrigeration purposes.

4. Condenser section: The condenser is a heat exchange tube located directly opposite the outlet pipe of the compressor, used to cool the refrigerant gas into the liquid refrigerant and release heat, playing a cooling role in the refrigeration cycle.

5. Expansion valve and evaporator: the expansion valve can flow the refrigerant evaporated at high pressure in the compressor to the low-pressure state, generating an endothermic reaction, so that the refrigerant can drive the generation of cold air in the evaporator.

The aircon PCB automates the adjustment, monitoring, and feedback of air temperature, flow rate, and humidity through a series of signal processing, driving electrical appliances, controller adjustment, and other processes. This enables rapid control of environmental temperature and humidity, ensuring user comfort and electricity safety.

The function of the aircon PCB

We need to oscillate the working condition of the crystal oscillator compared to how we usually swing, to generate frequency signals. Electrical appliances can only work normally with the signal flow, such as when people walk and their feet keep moving, to generate energy for people to move forward. The aircon PCB is the control center of the air conditioning system, used to collect signals from remote controls or sensors, and after processing, issue commands to components such as compressors and fan motors to operate appropriately.

Components in the aircon PCB

1: Transformer: A transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. Its main components are the primary coil, secondary coil, and iron core (magnetic core).

2: Remote control receiver head: The remote control receiver head is an integrated receiver module used in infrared remote control systems, with built-in PIN photodiodes and preamplifier ICs to achieve the pickup, amplification, and demodulation of infrared remote control receiver head LBST0038A. The detection output signal can be directly decoded by the microprocessor. Encapsulated with epoxy resin that can filter out visible light interference, it is not susceptible to environmental interference and can suppress the pulse output of uncontrolled signals.

3: Pressure connector: A pressure gauge connector is a connector used to connect the equipment or pipeline of the measured medium to the pressure gauge.

4: Electromagnetic valve lead connector: A hydraulic connector that can connect or disconnect pipelines without the use of other tools when connecting to an ultra-high-pressure hydraulic system.

How to detect faults in the  aircon PCB

Maintenance method for the power circuit of the aircon PCB: The fault characteristics of the power circuit of the aircon PCB are generally that the fuse is intact and burned as soon as the power is turned on. For the former fault, a multimeter can be used to measure whether there are 220V and 10-13V voltages in the primary and secondary stages of the transformer. If so, a multimeter can be used to measure whether there are+9-12V and+5V voltages in the DC stage of 7812 and 7805, to distinguish the fault location. For the latter, it indicates that there is a short circuit in the circuit. A multimeter ohmmeter should be used for resistance testing to determine the short circuit location of the circuit. At the same time, the split method can also be used for inspection. For example, the primary winding of the transformer can be disconnected and the machine can be powered on for a test run. If the fuse tube is also burned, it indicates that the fuse tube is burned due to the short circuit of the varistor or the ceramic chip capacitor. Otherwise, it is due to a short circuit of the transformer or rectifier tube.

Maintenance method of temperature sensing circuit of aircon PCB: the thermistor is a thermistor with a negative temperature coefficient, that is, the higher the temperature is, the smaller the resistance is; the lower the temperature is, the greater the resistance is; the resistance value is about 5-20K Ω at 25 ℃ (depending on the model). Therefore, a multimeter can be used to measure the resistance value of the thermistor to determine its quality. If the measured resistance value is infinite or very small, it indicates that the thermistor has been damaged.

Maintenance method for the relay circuit of the aircon PCB: First, distinguish whether the integrated power drive module is damaged or the relay is damaged. If the buzzer sounds after pressing the remote control, but the entire machine is not working, it is generally due to damage to the integrated power drive module; If only some functions are abnormal after startup, the relay may be damaged. At this time, it can be determined whether the relay coil is burnt out or the contact is stuck by listening to the sound of the relay's engagement. When the relay coil is burnt out, there is no engagement sound. The relay can also be judged by the ohm range of a multimeter. When disconnecting the power, first measure the coil resistance value. The normal resistance value is several hundred ohms. If it is infinite or zero, it indicates that the relay is damaged; Then measure the contacts, and if the resistance value is zero, it indicates that the contacts are sticking.

Maintenance method for the receiving circuit of the aircon PCB: Turn on the power and use a multimeter to measure the voltage between the power supply terminal and the signal terminal of the receiving head and the ground. The normal value should be+5V voltage at the power supply pole, and+2.5V voltage at the signal pole. Otherwise, it is abnormal. Common faults include damaged receiver heads or capacitor breakdowns.

Maintenance method for resetting the circuit of the aircon PCB: The reset voltage is a delayed rising voltage, which can be observed using the DC voltage range of a multimeter. If the observation is unclear, an oscilloscope can also be used to detect it. When using an oscilloscope to detect, there can be a baseline shaking, and then it becomes high, which is the starting process of the reset voltage. If no baseline jitter is seen, it indicates a fault in the reset circuit.

Maintenance method for the crystal oscillator circuit of the aircon PCB: Power on and start the machine. When normal, use a multimeter to measure the voltage at the two pins of the quartz crystal oscillator tube to be around+2.2V. If it is less than 1.5V, it means the circuit has stopped vibrating. Elsewhere, it can also be determined by removing the quartz crystal oscillator and using a multimeter's ohm gauge. A good quartz crystal oscillator should be open-circuit when measured with a multimeter. If a short circuit is found, it indicates that the crystal is damaged. For open circuit faults (broken wires or cracks), it is not possible to determine them with a multimeter, and alternative methods can be used to check them.

Maintenance method for the CPU chip of the aircon PCB: The necessary conditions for the normal operation of the air conditioning CPU are: power supply voltage+5V, reset voltage, and clock pulse signal. None of these three conditions are indispensable, otherwise, the CPU will not work properly. Therefore, a multimeter can be used to detect the voltage under its working conditions. If the voltage value is normal and the entire machine is not working, it can be determined that the CPU chip is damaged.

The aircon PCB is an important component of the air conditioner and is mainly responsible for controlling the operation of the air conditioner. It can not only ensure the normal operation of the air conditioner but also adjust the functions of the air conditioner according to the user's needs.