Product manual

17
ComPac 6/09-18
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.
Figure 5. H205A Control Point Adjustment
The controller modulates the position of the outside air damper in response to input from the enthalpy
and mixed air sensors. The controller is designed to maintain the supply air temperature between 50°
to 56°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 controller
will open the damper and admit outside air (i.e., economizer cooling). If the outdoor ambient is too
hot or humid, the controller 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.
D
C
B
A
54.4 Degrees
Between
Scaleplate
and Knob
Index Mark
on Controller
Flat on Shaft
Perpendicular
to Index Mark
on Controller