How to use a multimeter to find faults in electrical control circuits
There are generally two methods for finding circuit faults: voltage method and resistance method. The voltage method uses voltage measurement to detect fault points, while the resistance method uses resistance measurement to locate faults. They each have their own advantages. If you are not familiar with the circuit, we recommend using the resistance method to determine the fault, which is relatively safe.
Before measuring the control circuit, disconnect the power/fuse of the control circuit to separate it from the main circuit. The purpose of doing this is to avoid interference from the main circuit when measuring the control circuit.
Then place one probe at the odd starting number of the control circuit (such as 101) and another probe at the even starting number of the control circuit (such as 102), and the resistance between them should be infinitely large. Then press the button to switch SB2, and there should be a certain resistance value (the resistance value is equal to the coil resistance). If the resistance is still infinite, it means that there is no connection between the two probes or that there is a break somewhere, then continue to search further.
Then we press the button again and measure the resistance between the next terminal (103) of the starting terminal and the even starting number (102). If there is a certain resistance value, it indicates that there is an open circuit between 101 and 103. If the resistance is still infinite, it means there is still a circuit break somewhere between 103 and 102, then continue to search further.
Because the numbering rule determines that odd and even numbers are two different polarity circuits, we measure the terminals ending in odd and even numbers, and there is normally a certain resistance between them. (Of course, the premise is the same power circuit)
