Marvair ComPac Installation & Operation Manual
12/2017 Rev.16
19
Economizer changeover control – Dry Bulb Sensor
The dry bulb sensor only responds to the dry bulb temperature of the outside air and ignores the humidity.
The sensor has eight set points. The factory setting is 58°F (14.5°C). These set points can be changed
by moving the dip switches on the top of the dry bulb sensor. See Fig. 2.
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.
