Correctly diagnosing system faults is important to profitable service calls and to the reputation of technicians and their companies. Misdiagnosing a system can be problematic for technicians, their companies, and their customers. As a service technician, it is a good practice to try to verify that the diagnosis is correct. This is not always possible or easy to achieve, but it should be attempted. There are two basic ways to verify a diagnosis: 1) when possible, the suspect component can be temporarily jumped out, or 2) additional testing can be done to verify the findings.
Defective controls are the easiest to verify. Simply jumping out the suspect control will verify if it is the problem. Be careful — not all control components can be left jumped out. This is especially true of any safety control. It may be jumped out for a very short period just to verify the diagnosis, but it should not be left that way. Use good judgment when jumping out any component.