22
ComPac 9/04-12
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
delivered to the space by modulating the damper blade to "mix in" a quantity of inside air to
provide a constant 50° to 56°F. (Adjustable minimum potentiometer, part number 70012,
is optional.)
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
