Unico Tech Tip, Low Ambient

Burt Robertson, HVAC Marketing Manager

Since the Unico system operates at colder coil temperatures (in the cooling mode), an anti-frost switch is installed on the indoor coil to prevent coil freeze-up. In certain instances, such as when the outdoor ambient temperature is low, the condensing unit will cycle on the anti-frost switch. This may reduce the cooling capacity at a time when the cooling load is still fairly high. To provide better control and comfort install a low ambient control on the condensing unit. Typically, a low ambient control is necessary when operating the unit at outdoor temperatures below 80° F especially for a 5 ton nominal capacity system. This control modulates the outdoor blower to maintain a minimum liquid line temperature. Other controls may cycle the fan on/off. In either case, check with the condensing unit manufacturer to determine what controls are compatible with the condensing unit.