by Ron Walker
This system is controlled by a close on rise in temperature thermostat. The cooling thermostat will either be a mechanical type with a sensing bulb or a digital thermostat with a thermistor. Most of the walk-in coolers that require repair will be older and may have been retrofitted with a digital thermostat. Typically the thermostat is set to 35°F. As the temperature rises, the thermostat closes, applying power to the compressor which is energized by a current relay. The condenser fan is wired in parallel with the compressor and runs whenever the compressor is energized. The system may or may not have a contactor to provide power to the compressor. The evaporator fan(s) run continuously circulating cool air through the cooler whether or not the compressor is running. Unlike a residential air conditioning system, mild frost may be present on the evaporator coil. Mild frost is not a concern as the evaporator fan(s) continue to run when the compressor is in the off cycle. Circulating 35 to 39°F air over the evaporator coil. This, above freezing, air will melt the frost on the coil during the off cycle. This is called an off-cycle defrost system.
This system is controlled by a close on rise in temperature thermostat. The cooling thermostat will either be a mechanical type with a sensing bulb or a digital thermostat with a thermistor. Most of the walk-in coolers that require repair will be older and may have been retrofitted with a digital thermostat. Typically the thermostat is set to 35°F. As the temperature rises, the thermostat closes, applying power to the compressor which is energized by a current relay. The condenser fan is wired in parallel with the compressor and runs whenever the compressor is energized. The system may or may not have a contactor to provide power to the compressor. The evaporator fan(s) run continuously circulating cool air through the cooler whether or not the compressor is running. Unlike a residential air conditioning system, mild frost may be present on the evaporator coil. Mild frost is not a concern as the evaporator fan(s) continue to run when the compressor is in the off cycle. Circulating 35 to 39°F air over the evaporator coil. This, above freezing, air will melt the frost on the coil during the off cycle. This is called an off-cycle defrost system.