Diagnostic Strategies

DIAGNOSIS AND TESTING
Diagnosis is more than just following a series of interrelated steps to find the solution to a specific condition. It is a way of looking at systems that are not functioning and finding out why. Also, it is knowing how the system should work, and whether it is working correctly. Most qualified diagnosticians rely upon the same or similar basic procedures when searching for the cause of a concern.

There are basic rules for diagnosis. If these rules are followed, the cause of the objectionable condition or malfunction will usually be found the first time through the system.

Know the System
Know how the parts go together. Also, know how the system operates, what its limits are, and what happens when something goes wrong. Sometimes this means comparing a system that is working properly with the one being serviced.

Know the History of the System
How old or new is the system? What kind of treatment has it had? Has it been serviced in the past in such a manner that the present concern may be partially or totally caused by that prior service? What is the service history? A clue derived from any of these areas might save a lot of diagnosis time.


Know the Probability of Certain Conditions Developing
It is true that most conditions are caused by simple things rather than by complex things, and that inoperable conditions occur in a fairly predictable pattern. Electrical conditions, for instance, usually occur at connections rather than in components. An engine no-start is more likely to be caused by a loose wire or some component out of adjustment than a sheared-off camshaft. Know the difference between impossible and improbable. Many good technicians have spent hours diagnosing a system because they thought certain failures were impossible, only to eventually find out the failures were just improbable and actually had happened. Remember, new parts are just that, new. It does not mean they are good, functioning parts.


Don't Cure the Symptom and Leave the Cause
Recharging a refrigerant system may correct the condition of insufficient cooling, but it does not correct the original condition unless a cause is found and addressed. A properly working system does not lose refrigerant over time.


Be Sure the Cause is Found
Do not be fooled into thinking the cause of the concern has been found. Perform the proper tests, then double check the results. The system should be checked for refrigerant leaks. If no leaks are found, perform a leak test with the system under extremely high pressure. If the system performed properly when new, it would have to have a leak to be low in charge.