Which leak detection method is ineffective on refrigeration systems charged with zeotropic refrigerant?

The halide lamp method is ineffective on refrigeration systems charged with zeotropic refrigerants primarily due to the fact that these types of refrigerants often contain components that do not react with the halides in the lamp. Halide lamps work by burning a gas that produces a colored flame when in contact with refrigerants containing chlorine or bromine. However, zeotropic refrigerants, which consist of blends of different refrigerants, may not contain any halogens capable of creating a reaction that would be detected by a halide lamp.

In contrast, electronic leak detectors, ultrasonic leak detectors, and soap bubble tests are all versatile methods that can work effectively with zeotropic refrigerants. Electronic detectors can identify various types of refrigerants by sensing their specific chemical properties, ultrasonic detectors detect the sound of gas escaping from a system, and the soap bubble test can visually reveal leaks regardless of the refrigerant type. Thus, the ineffectiveness of the halide lamp specifically with zeotropic refrigerants is what makes it the correct choice for this question.