When a refrigeration system fails, many times the cause can easily be diagnosed. However there are occasions when the cause cannot easily be determined - either the true cause of the problem is unclear or the technician is unsure of a problem. In either case, this can be a very frustrating experience.
How can a technician work through these jobs? One method used by some technicians is to “read and record.” This means you measure and record all of the system’s possible operating conditions. This includes all possible refrigerant pressures, such as the pressure at the compressor’s inlet and outlet ports, the refrigerant pressure in the evaporator and condenser, and any other locations. Multiple pressure readings allow you to determine if any excessive pressure drops exist throughout a system.
Excessive pressure drops can cause a technician to assume an inaccurate pressure reading, which can lead to misdiagnosing a problem. For example, the refrigerant pressure at the outlet of the evaporator may not be the same at the inlet of the compressor. On a properly designed and installed system, the pressure drop across the suction line should equal no more than a 2°F change in the refrigerant’s saturation temperature. But what if the system is not properly designed and installed? What if there is a significant pressure drop across the suction line? Now if you read the pressure at the inlet of the compressor and try to calculate the refrigerant superheat value at the outlet of the evaporator, will your calculations be accurate? No.
All of the system’s temperatures need to be recorded such as the refrigerant temperature at the outlet of the evaporator, outlet of the condenser, inlet of the compressor, and outlet of the compressor. All air temperatures should be recorded such as the temperature entering and leaving the condenser and entering and leaving the evaporator, as well as any other necessary temperatures.
The compressor’s oil level and, if possible, the refrigerant level in the receiver should be included in these recordings. All of the system’s electrical conditions should be recorded, such as the applied voltage and amperage draw of all motors, especially the compressor. Record as much information as possible. The more, the better.
This procedure helps a technician in several ways. First, it forces him to look at the entire picture and not miss vital information that can help lead him to finding the problem. Second, it allows him to review the problem with a fellow technician or technical advisor.
When discussing the problem, a technician does not need to recall from memory any of the system parameters. Sometimes our memory fails us, and we give the wrong information, which masks the true problem. It also eliminates “the superheat is good” or “the amperage draw is normal” statements. Numbers do not lie, but your memory may fail you.
Reading and recording also has some benefits on functional systems. It allows the next technician to see how the system was operating previously, which can be a tremendous aid the next time the system fails. The next technician can compare the current operating parameters to the past parameters and may be able to discover the current problem. These records also can be saved and trended over time to help predict possible future system issues or schedule any required maintenance and/or repairs.
Reading and recording does take extra time. A technician must determine when it makes sense for the job and the customer. It is not needed on every job or for every customer, but it should be considered and used when appropriate and/or necessary.
Ice Breaker: Read and Record
July 4, 2011