A common problem with these cases is the evaporator coil icing up and causing the temperature within the case to rise. When the case is loaded with product, it is impossible to visually check the condition of the evaporator without removing some of the product from the bottom of the case. Doing this is a time-consuming task and often involves getting help from a store clerk.
Before going this route, a technician can measure the discharge air velocity at the honeycombs. If the velocity is within the manufacturer's specifications, it is likely that the coil is not iced up. However, if the velocity is lower than the manufacturer's specifications, it is an indication of a possible iced-up coil. In this event, the technician must remove the product to visually inspect the coil and identify the problem.
The electrical components on these cases, like all refrigeration cases, will need periodic servicing. Defrost heaters, evaporator fan motors, drain heaters, and other components may all require changing at some point.
The wiring leading to the various electrical components will be color-coded to allow a technician to troubleshoot the system more easily. Many of the electrical components are located in the same area as the evaporator. This would require removing some product to expose those components.
To make troubleshooting easier and the electrical connections safer, manufacturers will locate all of their electrical connections in the kick plate located on the bottom front of the cabinet. In this way, a service technician can use the color-coded wiring to identify the electrical wiring leading to the various components. The technician could then troubleshoot the problem without having to remove any product from the case.
HeatersManufacturers also incorporate door heaters into reach-in glass door freezers. There are usually several sets of door heaters used. One heater is located in the door's frame to prevent it from icing up and possibly causing the door to be frozen shut. Most often there is a heater in the door itself to prevent condensation from forming on the glass portion of the door. Again, by removing the kick plate and identifying the correct wires, a technician can check the operation of these heaters.
The refrigeration system is normally tied in to a parallel rack system located either on the roof or at the rear of the building. To ensure that the evaporator is fully active, a technician can measure the superheat at the outlet of the evaporator coil. An acceptable superheat setting for the thermostatic expansion valve on the cases is 3 degrees to 5 degrees F. This will ensure that the evaporator is being used to its fullest capacity and that there is no liquid returning to the compressors at the rack. When checking or adjusting the superheat setting, it is important to make sure the evaporator is not iced over and that the case is within 10 degrees F of its desired operating temperature.
When making any adjustments, be sure not to make an adjustment of more than 1/4- to 1/2-turn at a time. Once an adjustment has been made, let the system stabilize for a minimum of 15 minutes, then recheck the setting and make any additional adjustments.
Defrost SystemThe defrost systems on reach-in glass door cases can be either electric heater or hot gas. The design engineer decides on the type. The technician must be able to identify which defrost system is being used. Exposing the electrical wiring at the kick plate and inspecting it can aid in identifying the type of defrost system.
There are advantages to either system. Electric defrost systems normally will obtain a better and less problematic defrost. However, they are more costly to run. Hot gas systems are essentially cost-free, since they employ the system's hot gas to defrost the evaporator. But they are more problematic and can cause an incomplete defrost of the evaporator coil if not set up properly.
Defrost systems are usually set up as time initiated and temperature terminated. The location of the defrost termination sensor and its set point will differ from manufacturer to manufacturer, and is dependent on the type of defrost system used. The location and set point are important to ensure that the evaporator coil will be defrosted completely without overheating the case.
A technician may need to adjust the termination setting to allow the case to properly defrost. A common location for the defrost termination sensor is at the return elbow at the coil end opposite the thermostatic expansion valve.
On some electric defrost systems, it may be located upstream of the evaporator coil in the rear channel of the case. On some hot gas systems, it may be located on the dump line of the evaporator.
A typical setting for termination is 55 degrees to 60 degrees for hot gas systems and 65 degrees to 75 degrees for electric defrost. Again, the actual termination setting should be obtained from the manufacturer's specifications, as it will depend on the design and type of defrost system employed.
CleaningCleaning is an important task in keeping the case running efficiently with minimal breakdowns. Case cleaning will keep the drains from backing up. It also removes any ice that has developed over a period of time and is not being defrosted during the normal defrost cycle. Cleaning also ensures good airflow by keeping the honeycombs clean.
Case cleaning should be done on a regular basis. Refer to the manufacturer of the equipment for their specifications on cleaning a particular unit.
Cleaning should include removing all product and, with the electrical power disconnected from the case, rinsing down the entire evaporator section to remove any accumulated ice buildup. The honeycombs should also be cleared of any dirt. Once the case is cleaned, it should be left to dry for several hours before starting up the refrigeration system.
Servicing glass door reach-in freezers is not very involved. Knowing the basics and referring to the manufacturer's specifications will enable any technician to properly troubleshoot and efficiently repair these cases.
Joe Marchese is owner of Coldtronics, Pittsburgh. He can be reached at 412-734-4433, www.coldtronics.com, or firstname.lastname@example.org.
Publication date: 08/02/2004