A refrigeration system with an overcharge of refrigerant is an issue that almost all technicians have come across at some point in their careers. It’s the direct result of human error, and even the most seasoned technicians are bound to make mistakes every once in a while.
So, once the problem has occurred, how can it be solved? What are the best approaches when it comes to fixing an overcharged refrigerant system? Do rules of thumb and shortcuts cause more harm than good?
“This type of problem is still very common today, especially when a new system start-up needs to be field-charged or a major system component has been replaced and the system requires complete recharging,” said Dennis Silvestri, lead instructor, MRS Educational Training, New Haven, Connecticut. “Overcharging is also common when an existing system is converted from one refrigerant to another. A number of overcharging symptoms may occur, such as the high-side pressure will be higher than it should be, subcooling temperature will be higher than normal, and high condenser splits — the temperature difference between the ambient temperature and the condensing temperature of the refrigerant — will be present. Generally, subcooling can be between 10°-20°F and condenser splits between 10°-30°, depending on the efficiency of the condenser. Always check the manufacturer’s information on the unit being serviced.”
Joe Marchese, author, instructor and former HVACR contractor, said overcharging symptoms really depend on the system itself, “but if the system has a high pressure switch, it’s likely the system will shut down on this safety switch repeatedly.”
Joseph Adeszko, program coordinator of the HAC department at Moraine Valley Community College in Palos Hills, Illinois, said there are many ways to approach an overcharged system. “You can walk out to the condensing unit and feel the temperature of the air leaving the condensing unit,” he said. “An experienced technician can get a good feel if the air temperature seems high to them. Do a touch on the suction and discharge lines. A reciprocating compressor will be making a louder than normal noise as it struggles to pump the extra refrigerant.”
Adeszko also noted that not cooling properly is usually the reason a service call is made. “A technician can place the gauges on and will experience high suction and discharge pressures. They will also have a high amperage draw as the compressor is working harder than designed in order to pump the extra refrigerant.”
FINDING A SOLUTION
For Silvestri, it’s important to note that technicians shouldn’t be looking for the “quick fix” or trying to find the easiest way to get in and out of the job.
“Knowing that no one symptom could indicate a refrigerant overcharge, this kind of problem should be diagnosed like you would any other service call,” he said. “Understand the type of system that’s being worked on, what you see, and what is occurring when the unit is operating? The customer may be able to provide information as to what they may have seen or heard when the unit was operating. In addition, copies of past service calls should be available. These could be on file with the current servicing company or possibly provided by the customer. Look them over to get an idea as to what work has been done on the equipment. All of these will provide information to the service technician to help provide a starting point for the technician to take. High- and low-side pressures along with key temperature readings, like superheat and subcooling, are invaluable to the service technician.”
Examining both sides of the system is an important part of the process, according to Marchese. “That includes the system’s high and low side pressures as well as the evaporator’s superheat and condenser subcooling values,” he said.
Marchese and Adeszko both noted there are no real shortcuts to diagnosing an overcharged system.
“A technician needs to gather data to properly troubleshoot a unit and then evaluate the data to see where the issue may be,” said Adeszko. “You need a number of data, including subcooling, superheat readings, compressor amp draw, delta T, and wet bulb temperatures. Those should be compared to the manufacturer’s specifications.”
With today’s blended types of refrigerant and issues with refrigerant fractionation, Silvestri said technicians also need to weigh in the proper amount of refrigerant.
“Package or self-contained systems have the amount of refrigerant required right on the unit’s data plate,” he said. “Generally, they do not require field-charging on new system start-ups. Remote or split systems’ data plates indicate how much refrigerant is necessary for the evaporator and condensing sections and how many additional ounces of refrigerant are required for each foot of liquid line. This type of system requires field-charging and is more prone to having the system overcharged as well as undercharged.”
Silvestri also noted that besides weighing in the refrigerant charge, many manufacturers provide charging charts that indicate what high- and low-side pressure readings the system should have based on various outdoor and indoor temperature conditions. They may also provide subcooling and superheat information, as well.
“This type of unit information does work, as long as the service technician understands how to use it and is willing to use it,” he said.
Adeszko noted that while this issue may not be quite as prevalent as it once was throughout the industry, it is a problem that will never go away.
“The mom and pop shops have gone away, and the new technicians entering the field are better trained on proper procedures. Still, there will always be overcharged systems. We all make mistakes.”
Editor’s note: The NEWS’ Trainers Panel consists of some of the best HVAC educators, instructors, and trainers from across North America. Their insights are used to answer technical questions from the field and suggest solutions to everyday problems faced by technicians. They detail proper maintenance techniques, solve troubleshooting issues, and find solutions to difficulties that are seen from coast to coast. If you’re interested in becoming a member of the panel, contact The NEWS’ products and education editor, Nick Kostora, at firstname.lastname@example.org.
Publication date: 11/21/2016