47
Outdoor Air Temperature (OAT) Sensor
The outdoor air temperature sensor (HH57AC074) is a 10 to
20 mA device used to measure the outdoor-air temperature.
The outdoor-air temperature is used to determine when the
EconoMi$er IV can be used for free cooling. The sensor has 8
selectable temperature changeover setpoints, ranging from
48°F to 78°F. The temperature changeover is set using the
3 dip switches on the sensor See Fig. 60.
Fig. 60 — C7660 Temperature Sensor
Supply Air Temperature (SAT) Sensor
The supply air temperature sensor is a field-installed 3 K
thermistor and is installed through the heat section partition ex-
tending into the supply airstream. See Fig. 61. The operating
range of temperature measurement is 0°F to 158°F (–18°C to
70°C). See Table 6 for sensor temperature/resistance values.
Fig. 61 — Supply Air Temperature Sensor Location
The temperature sensor looks like an eyelet terminal with wires
running to it. The sensor is located in the “crimp end” and is
sealed from moisture.
Outdoor Air Lockout Sensor
The EconoMi$er IV is equipped with an ambient temperature
lockout switch located in the outdoor airstream which is used
to lock out the compressors below a 42°F (6°C) ambient tem-
perature. See Fig. 56 on page 44.
ECONOMI$ER IV CONTROL MODES
Determine the EconoMi$er
®
IV control mode before set up of
the control. Some modes of operation may require different sen-
sors. The EconoMi$er IV accessory is supplied from the factory
with a supply-air temperature sensor and an outdoor-air tempera-
ture sensor. This allows for operation of the EconoMi$er IV with
outdoor air dry bulb changeover control. Additional accessories
can be added to allow for different types of changeover control
and operation of the EconoMi$er IV and unit.
Outdoor Dry Bulb Changeover
The standard controller is shipped from the factory configured
for outdoor dry bulb changeover control. For this control mode,
the outdoor temperature is compared to a selectable set point on
the OAT sensor. If the outdoor air temperature is above the set
point, the EconoMi$er IV will adjust the outdoor air dampers to
minimum position. If the outdoor air temperature is below the
set point, the position of the outdoor air dampers will be con-
trolled to provide free cooling using outdoor air. When in this
mode, the Free Cool LED next to the outdoor enthalpy set point
(ABCD) potentiometer will be on. The changeover temperature
set point is controlled by the dip switches on the sensor. See
Fig. 62 for the switch positions corresponding to the temperature
changeover values. The ABCD potentiometer on the controller
should be turned fully clockwise (CW) to the “D” position. See
Fig. 64 for static pressure drop.
Supply Air Temperature Sensor
Table 6 — Supply Air Sensor
Temperature/Resistance Values
TEMPERATURE (F) RESISTANCE (ohms)
–58 220,250
–40 100,000
–22 53,010
–4 29,091
14 16,500
32 9,795
50 5,970
68 3,747
77 3,000
86 2,416
104 1,597
122 1,080
140 746
158 525
176 376
185 321
194 274
212 203
230 153
248 116
257 102
266 89
284 70
302 55
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