Pre Diagnosis Inspection

DIAGNOSIS AND TESTING
Diagnosis is more than just following a series of interrelated steps in order to find the solution to a specific condition. It is a way of looking at systems that are not functioning the way they should and finding out why. Also, it is knowing how the system should work and whether it is working correctly. All good diagnosticians use the same basic procedure. There are basic rules for diagnosis. If these rules are followed, the cause of the condition 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, its limits and what happens when something goes wrong. Sometimes this means comparing a system that is working properly with the one you are servicing.

Know the History of the System
Has it been serviced in the past in such a manner that might relate to the present condition? What is the service history? A clue in 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 ones and they occur in a fairly predictable pattern. Electrical concern 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.

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 concern unless a cause is found. 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 have been checked for refrigerant leaks. If no leaks were found, perform a leak test with the system under extremely high pressure.