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30
Supply Air Temperature (SAT) — A supply air temperature
sensor is required for certain control types discussed in the sec-
tion Capacity Control, beginning on page 64. The sensor is
field-installed in the indoor unit and wired to the low voltage
terminal (LVT) of the unit to measure the air temperature leav-
ing the evaporator coil. Sensor wiring should not be in conduit
with other control voltages, or erroneous or erratic readings
may result.
The sensor must be mounted in the discharge of the unit,
downstream of the cooling coil and before any heating coil or
heat exchanger if reheat is utilized. See Fig. 24. Be sure the
probe tip does not come in ontact with any of the unit
surfaces.
The SAT sensor (Part No. 33ZCSENSAT) consists of a
thermistor encased within a stainless steel probe. See Fig. 25.
The SAT sensor probe is 6 in. (150 mm) nominal length with
114 in. (2.9 m) of unshielded, 2-conductor 18 AWG twisted-
pair cables. Wiring to the device must be field-supplied.
Shielded 2-conductor, 18 AWG twisted-pair cabled is required.
The sensor temperature range is –40 to 245 F (–40 to 118 C)
and is a Type II thermistor with a nominal resistance of 10,000
ohms at 77 F (25 C). The sensor has an accuracy of ±0.36 °F
(±0.2 °C).
As an alternative to a single thermistor, an averaging sensor
(Part No. HH79NZ041) can be utilized to provide the supply
air temperature to the 38AP controls. See Fig. 26. This sensor
consists of 9 individual sensors wired within a 24 ft (7.3 m)
flexible copper tube. Wiring to the device must be field sup-
plied. Shielded 2-conductor, 18 AWG twisted-pair cabled is re-
quired. The sensor temperature range is –40 to 245 F (–40 to
118 C) and is a Type II thermistor with a nominal resistance of
10,000 ohms at 77 F (25 C). The sensor has an accuracy of
±0.36 °F (± 0.2 °C).
In lieu of wiring a sensor to the 38AP controls, the SAT sen-
sor reading can be broadcast to the unit. It is recommended
that the broadcast frequency be at least once every 30 seconds.
If a broadcast is not received for 3 minutes a thermistor failure
alert will be generated. The broadcast should write to the CCN
point, SUPPLY_T. Even though the SAT temperature is being
broadcast, a thermistor type
Configuration
o
OPT1
o
SAT.T
(SAT Thermistor Type) must be set to
0
(5,000
:
) or
1
(10,000
:
).
Fig. 25 — 33ZCSENSAT Sensor
.39
.08
FOAM GASKET
.40'' O.D.
.250
±
.01 Dia
5.5
±
.5
PLENUM RATED CABLE
114''
±
6
3.00
3.90
.175 DIA
x .600
NOTE: All dimensions
shown in inches.
END VIEW
COVER
TOP VIEW, NO COVER
SIDE VIEW
0.5 (12.7) CONDUIT
KNOCKOUT (X10)
TYPICAL
1.58 (40.08)
FOAM PAD
COPPER
TUBING
AVERAGING
HANDLE
SHRINK
TUBING
1.98
(50.26)
2.13
(54.10)
4.00
(101.60)
0.19 (4.76)
0.75 (19.05)
0.38 (9.53)
3.08 (78.23)
3.88 (98.60)
0.18
(4.69)
0.43
(10.99)
4.20
(106.67)
2.33
(59.08)
Fig. 26 — HH79NZ041 Averaging Sensor