If there is a low-temperature application of the evaporator with dry-coil-type units, then defrosting can be obtained. This is done by providing arrangements for the intake of outside air and the exhaust of this air to the outside during the defrosting period. Keep in mind that the outside temperature must be above 35°F when using this defrosting method. At very low temperatures, hot-gas defrosting may be employed. But, only when there is more than one evaporator connected to a condensing unit. This is so that the other unit can continue to provide refrigeration to the fixture.
When the operating conditions, such as designfixture temperature, operating refrigerant temperature, and condensing-unit running time, will allow, the removal of frost on the evaporator may be accomplished automatically. Controls normally supplied with condensing units by most manufactures will do this. By adjusting these controls, the condensing unit can be cycled to suit the job at hand.
