Measuring the evaporator’s superheat value is an important part of analyzing a system’s performance. If a lower-than-normal value is measured, too much refrigerant is entering the evaporator for the heat load. If a higher-than-normal value is measured, too little refrigerant is entering the evaporator for the heat load.
Bob and Tim were on their way to a no cooling call at a residence. They were pretty sure that it was a low refrigerant call. Bob said, “I hope that we can put the last lesson into practical practice. We have gone to a great deal of trouble to understand superheat.”
Bob and Tim were in the company conference room where Bob is set to give Tim some extra training at Tim’s suggestion. Bob said, “Tim, you asked for more explanation of what superheat is. This is not a very simple topic. It will take a couple of meetings to go into detail about it.”
While troubleshooting or installing refrigeration systems using a thermostatic expansion valve, it is a relatively common task to measure the superheat value of the refrigerant leaving the evaporator. However, there is a major consideration when using this measurement to analyze the operation of a system.
Actually, frost on the suction line only indicates that at the location where the frost is present, the suction line piping is below the dew point temperature of the surrounding ambient air and at or below 32°F. That’s it. It is neither an indication of a properly operating system nor a system defect.