Outdoor-Air Temperature Sensor (Fig. 19) Ð

The outdoor-air temperature (OAT) sensor is shipped inside the fan section. The OAT sensor continuously monitors the temperature of the air outside the building. The integral shield prevents ice formation on the sensor conductors. A ®eld- supplied conduit junction box is required for installation. See Fig. 20.

Position the OAT sensor so that it accurately senses only the outdoor-air temperature. The sensor must be located up- stream from outside air dampers and located where it is un- affected by interior and duct temperatures. During the unoc- cupied (fan off) period the sensor's location should have a minimal effect on its readings.

Do not mount the sensor in direct sunlight. Inaccurate read- ings may result. It may be necessary to ®eld-fabricate a shield to protect the sensor from direct sunlight.

Do not mount the sensor near the exhaust from air- handling units or compressors, or near leakage drafts of in- door air, or near shrubbery or trees. Inaccurate readings may result. Do not mount under direct water runoff. Water may freeze around the sensor in winter and produce a false reading.

If sensor wire is shielded, strip back the sensor shield and tape it to prevent contact.

Position the sensor with the slotted end pointed downward.

The ®eld-supplied junction box housing must be threaded to screw onto a male 1¤2-in. NPT electrical metal tubing (EMT) conduit adaptor. The assembled box and sensor must be mounted parallel to the building wall. See Fig. 20. The sensor can also be installed on a roof or other location.

For distances up to 500 ft, use 2-conductor 20 AWG cable to connect the sensor to the PIC terminals. Refer to the Field Wiring Connections section, page 52 for further wiring in- structions. See Table 4 for thermistor resistance according to temperature value.

Table 4 Ð Thermistor Resistance vs

Temperature Values for Outdoor-Air

Temperature Sensor

RESISTANCE

TEMPERATURE

RESISTANCE

TEMPERATURE

(Ohms)

(F)

(Ohms)

(F)

168,250

−40

5,000.0

77

121,350

−31

4,028.5

86

88,500

−22

3,265.0

95

65,200

−13

2,663.3

104

48,535

−4

2,185.0

113

36,476

5

1,801.5

122

27,665

14

1,493.0

131

21,165

23

1,244.0

140

16,325

32

1,041.5

149

12,695

41

876.0

158

9,950

50

739.5

167

6,245

68

627.5

176

Fig. 19 Ð Outdoor-Air Temperature Sensor

(P/N HH79NZ023)

Fig. 20 Ð Outdoor-Air Temperature

Sensor Installation

Mixed-Air Temperature Sensor Ð The optional mixed-air temperature sensor (MAT) is factory wired and installed on all units with a factory-installed mixing box (MXB), ®lter mixing box (FMB), or air blender (AMX). On units without an AMX, MXB, or FMB, the optional MAT is pack- aged and shipped inside the fan section for ®eld installation.

The ®eld-installed MAT should be mounted downstream of the return air duct and ®lters, but as close as possible to the 39L or 39NX unit.

AVOID repeated bending of copper tubing, as this will place stress on the sensor element and lead to eventual breakage.

DO NOT fold or crimp copper tubing.

USE CARE in forming and securing the element.

STRIP back and tape the shield in order to prevent contact.

Mount ®eld-installed MAT as follows (Fig. 21):

1.Punch a 1-in. diameter hole in the duct and feed the sen- sor element through the hole. Mount the utility box on the outside of the duct.

2.Bend the copper tubing surrounding the sensor element to conform to the area of the duct. Do not bend it to less than 21¤2 in. diameter on any turn. The sensor element should be evenly distributed over the entire cross sec- tional area of the duct.

Existing support structures may be used for the sensor element, as long as there is no metal-to-metal contact with the copper tubing, and the mounting does not interfere with other functions.

3.Use a ®eld-supplied plastic spacer, clamp, and screws to secure the sensor in the airstream. See Detail A, Fig. 21.

4.Using 2-conductor 20 AWG plenum-rated cable, connect the sensor to the PIC control box terminals.

42

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Image 42
Carrier 39L specifications Resistance Temperature, Ohms

39L specifications

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