When troubleshooting a refrigeration system, sometimes it helps to go back to the basics. Remembering that HVAC systems are dynamic devices with multiple components that all work together can help identify some common defects. Some problems may change one operating condition — for example, suction pressure — in a similar way, but usually another condition, such as evaporator superheat heat, will be different. Looking at multiple operating conditions during the troubleshooting process allows a tech to determine the true problem.
Too often, we try to troubleshoot a system by looking only at one operating condition. We then guess at the problem, sometimes we guess right, and sometimes we guess wrong. In any case, it is a guess, which is not a great method of troubleshooting. There are many times where a problem in one area can be caused by several different issues.
For example, a lower than normal suction pressure on a system can be caused by a low refrigerant charge, but it also can be caused by low heat load placed on the evaporator — either caused by an airflow issue or an iced evaporator. If you only looked at the system’s suction pressure, you may not know the exact cause of the problem. However, if you looked at the suction pressure and evaporator superheat, you would be able to easily determine the real problem. A system with a low refrigerant charge will have a lower than normal suction pressure coupled with a higher than normal evaporator superheat. A system with a low heat load on the evaporator will also have a lower than normal suction pressure, but can have either a normal or lower than normal evaporator superheat value.
A system with an excessive amount of refrigerant (overcharged) will have a higher than normal discharge pressure coupled with a higher than normal condenser subcooling value. A system with a dirty condenser will also have a higher than normal discharge pressure, but the condenser’s subcooling valve will be relatively normal. If we only look at the elevated discharge pressure, we may not be able to really determine the true cause of the problem.
So, why do we take shortcuts when it comes to troubleshooting? There can be several different reasons, but the most common is probably because we just get lazy. It takes extra steps to get these additional measurements. We either have to go get the right tool, or we need to remove a panel or some product to get to the right location. We’ve all been there — myself included — low suction pressure, just add some refrigerant; discharge pressure is too high, just take out some refrigerant. Sometimes we get lucky and the problem is solved. But, sometimes, we don’t get lucky, and not only do we not fix the problem, we create an additional problem for ourselves and the customer.
So, the next time you’re faced with a choice of whether you should take some extra time and additional measurements, do the right thing. Take the time to do it right and find the true problem the first time.
Publication date: 4/11/2016