Lennox LHT Series Service Manual page 17

Relative Humidity Sensor - Optional
The indoor relative humidity sensor (A91) is an analog
sensor with a 0-10VDC output over a relative humidity
range of 0-100% relative humidity. The sensor is powered
with 24VAC.
Enthalpy Sensor - Optional
The optional enthalpy sensors (A7 and A63) used with
the economizer have an output of 4-20mA. The sensor is
powered with 18VAC provided by M3 unit control.
Temp. °F (°C) Resistance +/-2% Temperature °F (°C) Resistance +/-2%
-40 (-40)
-20 (-28.9)
0 (-17.8)
20 (-6.7)
30 (-1.1)
Room Sensors
Room sensor (A2) is a two-wire thermistor with 1k series resistor.
Temp. °F (°C) Resistance +/-2%
40 (4.4)
45 (7.2)
50 (10)
55 (12.8)
Carbon Dioxide Sensor
The indoor carbon dioxide sensor (A63) is an analog sensor with a 0-10VDC output over a carbon dioxide range of 0-2000
ppm as shown in the following table. The sensor is powered with 24VAC.
Carbon Dioxide DC Voltage
PPM
0 0
200 1
400 2
Resistance vs. Temperature
335,671 40 (4.4)
164,959 50 (10)
85,323 60 (15.6)
46,218 70 (21.1)
34,566 80 (26.7)
Two-Wire Thermistor
Temperature °F (°C)
27,102 60 (15.6)
23,764 65 (18.3)
20,898 70 (21.1)
18,433 75 (23.9)
Carbon Dioxide Range
Carbon Dioxide
PPM
600
800
1000
Economizer Differential Pressure Sensor - Optional
Rooftop units installed with Smart Airflow™ will have a
Pressure Transducer (PT5) present in the economizer.
PT5 requires 5VDC power supply (P266-5 and {P266-
6) and gives 0.25 VDC to 4 VDC output (P266-4) corre-
sponding to 0" water column and 2" water column respec-
tively. For all practical purposes the output should be less
than 1.2" water column if not an error code is stored and
service alarm output is turned on.
Temperature Sensors
The return air (RT16) and discharge air (RT6) duct probes
and the outdoor air (RT17) are all two wire thermistors.
The resistance vs. temperature table is shown below:
TABLE 1
26,106
19,904
15,313
11,884
9,298
TABLE 2
Resistance +/-2%
16,313
14,474
12,882
11,498
TABLE 3
DC Voltage Carbon Dioxide
PPM
3 1200
4 1400
5 1600
Page 17
Temp. °F (°C) Resistance +/-2%
90 (32.2)
100 (37.8)
120 (48.9)
130 (54.4)
Temp. °F (°C) Resistance +/-2%
80 (26.7)
85 (29.4)
90 (32.2)
DC Voltage Carbon Dioxide
PPM
6 1800
7 2000
8
7,332
5,826
3,756
3,047
10,299
9,249
8,529
DC Voltage
9
10