The unit control switch may be located on top of the cabinet or on one of the sides, depending upon the particular design. The control switch is usually of the knob- or rotary-control dial type and normally has four positions, marked OFF, FAN, COOL, and EXHAUST. The damper controls are usually marked SHUT, VENT, and OPEN. To provide cooling, the switch dial is turned to the COOL position, and the damper dial to SHUT or VENT depending on whether or not outside air is desired.
To operate the unit as a ventilator, the switch dial is turned to FAN and the damper dial is turned as far open as desired. In the OPEN position, the unit passes in 100 percent of outside air. To exhaust room air, the switch is turned to the EXHAUST position, and the damper dial is turned to the VENT position. When a thermostat is installed for automatic cooling, the compressor and fans will cycle according to dial requirements.