18
Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
09/2021 Rev.15
Figure 2. Dry Bulb Sensor
Once either the enthalpy or dry bulb sensor has determined that the outside air is suitable for cooling,
the damper will open. The mixed air sensor will limit the air temperature delivered to the space by
modulating the damper blade to mix warm indoor air with cooler outdoor air to provide a constant
50°F to 56°F (10°C to 13.5°C)
Mixed Air Sensor:
The mixed air sensor is a thermistor mounted on a bracket adjacent to the right side of the blower
assembly. The thermistor senses the air temperature entering the structure, and provides a signal to the
economizer controller for modulating the position of the damper.
Minimum Position Potentiometer (W2 jumper):
The potentiometer controls the amount of outside air introduced in the building when the economizer
damper closes or the air conditioner is Off or in Mechanical Cooling. The factory setting is for the
damper to close completely when the unit is off or in Mechanical Cooling. (Pins 1 & 2 are jumpered)
If outside air is desired during mechanical cooling or whenever the indoor blower is running, jumper
pins 2 & 3. Refer to item 8 in Figure 4 for the location of the jumper.
If the potentiometer is enabled, the next step is to select how much outside air should be brought into
the building.
The potentiometer is adjustable from 0% to 100%. Setting the potentiometer to MIN means that the damper
will close completely and NO outside air will be brought into the building. Setting the potentiometer
to MAX means that the damper stays in the full OPEN position at all times. Factory setting is 50%.
