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Marvair Classic AVPA/HVPA/HVPSA Heat Pump I&O Manual
11/2017 Rev. 7
mixed air sensors. The controller is designed to maintain the supply air temperature between 50
o
to 56
o
F
by mixing warm indoor air with cooler outdoor air.
On a call for cooling from the wall-mounted thermostat, if outdoor conditions are suitable, the sensor will
open the damper and admit outside air (i.e., economizer cooling). If the outdoor ambient is too hot or
humid, the sensor will place the actuator in the closed or minimum open position and activate mechanical
cooling. The compressor is locked out during the economizer cooling mode.
Figure 2 - Enthalpy Sensor Temperature Control Points
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. Nominal resistance of the sensor at
77°F is 3000 ohms.
