The old saying, “When in doubt, change it out,” is not a good motto for HVACR service technicians. Guessing at a problem and randomly changing out components is never a good strategy, and it seldom works out well for the customer or the technician. Instead, technicians should strive to prove out their diagnosis and only changeout truly defective components. This can sometimes be accomplished by either temporarily jumping out the suspect component, bench testing the component, or performing an additional test to prove it is truly defective.
Defective controls are the easiest to verify. Simply jumping out the suspect control will verify if it is the problem. Be careful, though, because not all control components can be left jumped out. This is especially true of safety controls — they may be jumped out for a very short period to verify a diagnosis, but cannot be left that way. Use good judgment when jumping out any component.
Mechanical components are more difficult to verify since they cannot simply be jumped out. However, a technician often can verify a diagnosis by performing an additional test. For example, if a single-phase compressor fails to start and the technician has measured the correct voltage and resistances at the compressor, he or she may determine the compressor has internally locked up. This may well be true. However, the starting relay or start capacitor (where used) also may cause the compressor not to start. The technician should attempt to start the compressor with his own starting kit. If the compressor still fails to start, then the technician can be comfortable it is defective.
Repairing refrigerant leaks and verifying that a system is leak-free is important but not always easy. Sometimes, there is more than one refrigerant leak in a system. If a technician finds one leak, repairs it, and charges the system, he could be back on the job again shortly looking for another leak. This is costly for the technician and the customer.
There are two ways a technician can verify a system is leak-free. One is a standing pressure test. After all the refrigerant has been removed, dry nitrogen is introduced into the system and observed over a period of time. If the pressure remains the same, the system can be assumed to be leak-free.
A tech may also pull a deep vacuum on the system. Using an electronic micron gauge, pull a vacuum on the system down to approximately 500 microns. Once this level is achieved, the system is left idle. Observe your micron gauge — if the gauge reading begins to rise and steadily continues to rise, there is another leak in the system. If the micron gauge rises for a brief time and then levels off, it may mean the leak was repaired but the system may still contain moisture and will need to be dehydrated further. In this case, the technician simply continues to pull a vacuum on the system and repeats the test.
Verifying a diagnosis will take additional time, but this is time well spent. It will actually save time and money for both the technician and the customer by reducing the amount of callbacks and reducing the replacement of non-defective components on the job. It will also allow the technician to leave the job with peace of mind, knowing he has made a correct diagnosis.
Instead of “When in doubt, change it out,” think: “When in doubt, prove it out.”
Publication date: 3/7/2016