Carrier 40UV Installation, Start-Up And Service Instructions Manual page 30

OUTDOOR-AIR TEMPERATURE (OAT) SENSOR — The
OAT sensor is factory-installed and factory-wired to the con-
trol. The OAT sensor monitors the temperature of the outside
air entering the unit. See Fig. 13.
The sensor is installed immediately upstream from the
outdoor-air damper where it will accurately sense the tempera-
ture of the outdoor air entering the mixing box. The sensor con-
nects to the control module T7 and T8 (OAT) as shown in
Table 11.
The thermistor has a range of –40 to 245 F and a resistance
of 5,000 ohms at 77 F. See Table 13 for thermistor resistance
according to temperature value.
MIXED-AIR TEMPERATURE (MAT) SENSOR — The
mixed-air temperature (MAT) sensor is factory-supplied,
factory-installed, and factory-wired with each unit. The MAT
measures the temperature of air in the mixing plenum area.
The MAT connects to terminals T5 and T6 on the con-
trol module using 1 / -in. female quick connect terminals. See
4
Table 11.
The sensor uses multiple thermistor elements. This sensor
provides both mechanical and electrical averaging to achieve
an accurate, average temperature measurement over the entire
element length. Polarity is not a consideration. See Table 12 for
resistance vs temperature values. The sensor is installed in the
mixing plenum before the filter so it can sense the average air
temperature. See Fig. 14.
The MAT has range of –40 to 245 F with a nominal resis-
tance of 10,000 ohms at 77 F.
LOW-LIMIT THERMOSTAT — The low-limit thermostat
(LLT) is factory-installed and factory-wired on all units with
water coils. The thermostat is used to protect the water coils
from freezing temperatures in the event of a malfunction by
detecting the status of a potentially damaging condition.
The LLT is a 12-ft capillary tube mounted in the air stream.
See Fig. 15.
The LLT provides a SPDT contact. The contact provides a
sensor status indication to the control module and an electrical
interlock to the fan and water valves. Upon detection of a fault
condition, the unit ventilator will stop the fan, close the
outdoor-air damper, and position water valves as specified in
the sequence of operation. The LLT is factory set to trip at 38 F.
The temperature setting is non-adjustable. The switch will
automatically reset and restart the fan after its temperature has
risen by at least 5° F.
Table 13 — Thermistor Resistance vs Temperature
Values for Outdoor-Air Temperature Sensor
RESISTANCE
(Ohms)
168,250.0
121,350.0
88,500.0
65,200.0
48,535.0
36,476.0
27,665.0
21,165.0
16,325.0
12,695.0
9,950.0
6,245.0
5,000.0
4,028.5
3,265.0
2,663.3
2,185.0
1,801.5
1,493.0
1,244.0
1,041.5
876.0
739.5
627.5
TEMPERATURE
(F)
–40
–31
–22
–13
–4
5
14
23
32
41
50
68
77
86
95
104
113
122
131
140
149
158
167
176
30
The LLT is designed to trip if any 1-ft section of the capil-
lary tube senses cold air at or below the thermostat setting. The
temperature must exceed 43 F for the thermostat to automati-
cally reset to restore the circuit to normal operation.
REFRIGERANT LOW-LIMIT THERMOSTAT — The re-
frigerant low limit thermostat (LLR) is factory-installed and
factory-wired on all units with direct expansion coils. The ther-
mostat is used to protect the water coils from freezing tempera-
tures in the event of a malfunction by detecting the status of a
potentially damaging condition.
The LLR is a 18 in. capillary tube mounted in the air stream.
See Fig. 15.
The LLR provides a SPDT contact. The normally closed
contact is connected in series with the direct expansion relay
coil, such that the DX (direct expansion) control relay is
deenergized in a fault condition. The LLR is factory set to trip
at 28 F. The temperature setting is non-adjustable. The switch
will automatically reset and allow direct expansion relay opera-
tion when the temperature has risen by at least 5° F.
Fig. 13 — Outdoor-Air Temperature Sensor
(Part No. HH79NZ055)
MIXED-AIR
TEMPERATURE SENSOR
Fig. 14 — Mixed-Air Temperature Sensor Installed
in Mixing Plenum (Part No. HH79NZ075)
Fig. 15 — Low-Limit Thermostat