Primarily, ice machines are nothing more than simple refrigeration units with a few differences. Only water and refrigeration are involved with a well-insulated, but unrefrigerated bin to store the ice chunks or flakes.
In the cube producing units, water enters a reservoir tank. It is then circulated by a water pump and then sprayed onto the extremely cold surface of the mold (evaporator) where a thin layer is frozen almost instantly (see fig. 128). Excess water is circulated back into the reservoir and the process is repeated. One thin layer forms at a time until the molds are filled. A thermostat (See fig. 130a) is installed close to the molds, when the ice formed in the molds become thick enough to touch the thermostat, power to the compressor is interrupted, and the circuit to a heating element is closed to loosen the ice from the molds, causing the cubes to fall into the storage bin (see fig. 128) This cycle is referred to as the harvest cycle.
into the storage bin (see fig. 128) This cycle is referred to as the harvest cycle. In the harvest cycle of units that use a hot gas defrost system, the compressor is not stopped. Instead, a solenoid valve opens and allows the hot gas from the compressor discharge line to circulate directly through the evaporator coil (bypassing the condenser and the refrigerant control) to loosen the ice. (See figs. 16 and 16a). Other ice machines operate by circulating water over a cold evaporator plate or over the molds by flowing through a perforated tube. In the harvest cycle of these smaller, and mostly residential units, a solid slab of ice falls onto a heated grid and thereby cut into cubes, and the cubes then fall into the storage bin.
Some ice machines produce flakes (see fig. 130). In this type of ice machine, water flows over a freezing cylinder (evaporator) with sharp, spiraling, cutting blades, called an auger. When a thin layer of ice is formed, the low temperature is detected by a sensor, causing a switch to close the circuit to a motor, which turns the cylinder, causing the ice to be shaved into flakes and expelled into the storage bin (see fig. 130).
Storage bins employ either of the following two methods to control the amount of ice accumulated:
1. Mechanical (a lever-operated control). This is an arm projecting into the bin. When the level of ice rises enough to lift the lever, the power to the unit is cut off by a switch connected to the arm until some of the ice is removed.
2. Thermostatic (a sensing bulb is installed near the top of the bin). When the ice level in the bin reaches the bulb, the contraction of the refrigerant within the bulb transmits pressure changes to the thermostat, causing a switch within the thermostat to open the main circuit to the unit, shutting off the system.
As the water level in the reservoir lowers, the water inlet float opens a valve to the water supply to allow the reservoir to refill. Water from the reservoir is pumped to the sprayer tube where it is sprayed onto the mold continuously and instantly frozen in thin layers. Run-off water is returned to the reservoir. Ice continues to build until it becomes thick enough to touch a sensor, at which time the low temperatures cause the sensor to shut off power to the compressor and water pump and to energize the electric defroster. As the evaporator heats, the ice cubes loosen and fall into the ice bin. The cycle is repeated until the level in the bin goes high enough to touch the sensing bulb. The low temperatures are then transmitted to the thermostat-operating mechanism, causing a set of contacts to open, disrupting the flow of power to the unit. At this point, the ice-making operation is stopped until some of the ice is removed from the bin.
When there is a complaint of little or no ice production, check the following:
1. Is there power available at the unit? Are circuit breakers on? And are fuses OK?
2. Is the problem caused by poor or no refrigeration?
3. Is there a water problem? Is enough water getting into the ice machine? Check the water-valve solenoid, water float, and hoses for corrosion and deterioration. Check for clogged water lines or filters and clean as necessary.
4. Is the problem due to faulty controls such as a thermostat or solenoid valve?
Follow these procedures to quickly troubleshoot the problem: Allow the unit to run for at least one cycle to see what happens. If it continues building ice and never goes into the harvest cycle, the problem is probably the thermostat or the molds have become too dirty and have lost their smoothness due to mineral buildup on the evaporator plate. In this case, clean the surfaces carefully and thoroughly, using the manufacturer’s recommended cleaning agents. If the smoothness cannot be restored, try spraying them with Teflon or replacing the evaporator plate if necessary.
Very often, the master water valve (sometimes located under a kitchen sink) may have been inadvertently shut off by the owner or an employee. Check to see if it is turned on and that the water float is in good working condition. Figure 131 shows a wiring diagram of a typical ice machine.