AUX Air Conditioner Repair Guide: Not Cooling (Varistor ZNR1 Damaged)
Analysis and Testing: After testing, it was found that the varistor ZNR1 on the circuit board is damaged.
Repair Method: Replace ZNR1 to eliminate the fault.
Warm Tips:
1. Varistor Protection
The varistor ZNR1 of this model is connected in parallel with the primary coil of the power transformer, forming a series circuit with the fuse to suppress surge voltage. Under normal voltage conditions, the resistance value of the varistor is very high, reaching the mega-ohm level, and the current passing through it is only in the microampere range, which can be ignored, remaining in an open circuit state without affecting the circuit operation. However, when the power supply voltage exceeds its designed breakdown voltage, its resistance suddenly decreases to several ohms or even 0.1 ohms, allowing instantaneous currents of thousands of amperes to pass through. The varistor immediately switches from cut-off to conduction. Since it is connected in parallel with the power supply, it quickly blows the power fuse to prevent the main circuit board from being damaged. In addition, when encountering slight instantaneous surges in the power grid, the varistor absorbs and buffers these surge waves. Moreover, during lightning strikes or switch operations in inductive circuits such as transformers, the generated instantaneous overvoltage causes the varistor's resistance to suddenly decrease, allowing large currents to pass through, acting as a diversion to protect the entire circuit. This function is called overvoltage protection. The symbol for varistors in circuit diagrams is commonly represented as ZNR.
2. Common Fault Phenomena and Repair Methods for Varistors
Common fault phenomena of varistors include explosion or burning, causing a short circuit in the circuit. These faults are often caused by improper selection of varistors, prolonged overvoltage in the power supply, accidental connection to high voltage (due to thunderstorms, wind, lightning, etc.), or poor component quality. Varistors are one-time-use components; after damage, they should be replaced along with the fuse in a timely manner. If only the fuse is replaced without replacing the varistor, other components on the circuit board may be damaged when overvoltage occurs again.
Data Source: Beijing AUX Air Conditioner Repair Center http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3486891.