There are a couple of basic ways you can verify your diagnosis.
When possible, the suspect component can be temporarily jumped out, or an additional test can be done to verify your analysis.
Defective controls are the easiest to verify. Simply jumping out the suspect control will verify if it is the problem. But 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 your diagnosis, but not left that way. You must use good judgment when jumping out any component.
Mechanical components are more difficult to verify since they cannot be simply jumped out. However, a technician can verify a diagnosis by performing an additional test. Let’s say a single-phase compressor fails to start. The technician has measured the correct voltage and resistance at the compressor. The technician may determine that the compressor has locked up internally.
This may well be true. However, the starting relay or start capacitor (where used) may also cause the compressor not to start. The technician should attempt to start the compressor with a starting kit. If the compressor still fails to start, then it can be assumed that it is defective.
Leak RepairsRepairing refrigerant leaks and verifying that the system is leak-free is important, but not always easy. Sometimes there is more than one refrigerant leak in the 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.
There are two methods to aid a technician in verifying that a system is leak-free.
1. The standing pressure test.
After all of 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, you may assume that the system is leak-free.
2. Pull a deep vacuum on the system.
Using an electronic micron gauge, pull a vacuum on the system down to approximately 500 microns. 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, you may have repaired the leak but the system may still contain moisture and needs to be dehydrated further. Continue to pull a vacuum on the system and repeat the test.
Verifying your diagnosis will take additional time, but it is time well spent. It will actually save time and money for both you and your customer.
Marchese is owner of Arctic-Air Refrigeration, Pittsburgh, PA.
Publication date: 10/01/2001