The electric controls are placed either on the top, side or front of the unit for convenience and style. Most units have two main electrical controls (1) a master control that starts and stops the fans and compressor, the occupant uses this control to choose the operation desired (cool, exhaust, heat or ventilate) and to select fan speed, (2) a thermostat control that adjusts the thermostat to cooler or warmer side.
The master control.
The master control is often called the selector switch or cooling and fan control. It controls the compressor motor, condenser fan motor and evaporator fan motor. When the control switch is in its COOL position, all motors operate and the complete unit functions as an air-conditioning unit. When the control switch is in the VENTILATE position, the evaporator fan works as ventilating fan. In the EXHAUST position, the condenser-blower motor operates drawing stale air from the room as does an exhaust. The damper control must be at its similar position to allow the air to flow either out or in.
The Thermostat control.
The thermostat element in room air-conditioners is usually located in the returned air stream near the filter. The thermostat control is wired in the series with the starting relay that controls the compressor motor. Thus both the thermostat control and master control govern compressor operation.