Who is correct if Technician A uses a DMM to test the resistor block for opens while Technician B tests it with a lab scope?

Using a Digital Multimeter (DMM) to test the resistor block for opens is a standard procedure in diagnosing electrical issues, particularly in automotive or HVAC systems. A DMM is effective for measuring voltage, current, and resistance, making it a reliable tool to check for an open circuit, which occurs when there is a break that prevents current from flowing through the resistor block.

Testing the resistor block with a DMM allows the technician to specifically measure the resistance across the resistor terminals, ensuring that the component is functioning correctly. If the resistor shows infinite resistance, or an "open" reading, it indicates that the resistor is defective and needs replacement.

While using a lab scope can provide a visual representation of waveforms for more complex diagnostics, it is generally not required for a straightforward open circuit test. A lab scope excels in analyzing dynamic signals and is more suited for defects or issues that require a deeper analysis of signal patterns or transient behaviors. This means that while Technician B's approach can yield useful information, it may not be the most appropriate tool for simply testing for opens in the resistor block.

Therefore, Technician A's method of testing with a DMM is accurate and aligns well with the objective of diagnosing the condition of a resistor block effectively.