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3.5. Electric Heat Operation—Electric / Electric Units
3.5.1. Electric Heat Stage Delay Operation
First-stage heating demand energizes first-stage electric heat (K15 and K17). Second-stage heating demand energizes
second-stage electric heat (K16 and K18). When first-stage and second-stage heating demands are simultaneous, a delay
will occur between stage one and two (Parameter 62). Default delay is 12 seconds. Optional range setting is 12 to 60
seconds.
Go to SETTINGS > RTU OPTION > EDIT PARAMETER = 62 (HT ELEC STAGE DELAY)
3.5.2. Primary or Secondary Limits
If an electric heat limit (S15 or S63) opens, electric heat is de-energized.
If an electric heat limit opens three times (default) during a thermostat cycle, in addition, the service alarm output will
turn on. Valid options for Parameter 61 are 1 through 15.
Go to SETTINGS > RTU OPTION > EDIT PARAMETER = 61 (HT ELEC MAX LT OCC)
4. Sensors
The M3 Unit Controller is only compatible with L-Connection sensors provided with the unit or purchased separately as
specified in the Product Specification.
IMPORTANT
All 0-10VDC sensors require two separate twisted pair cables with shield. One cable is used for the 24VAC power and
one cable is used for the 0-10VDC output. Room sensors require a single twisted pair cable with shield. The shield drain
wires must be connected to the common at the unit field wiring terminal block only. The shield drain wires must not be
connected to common at the sensor. Non-communicating temperature sensors require single twisted pair wire only.
4.1. Temperature Sensors - Provided With Unit
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:
Temp. °F (°C) Resistance +/-2% Temperature °F
(°C)
Resistance +/-2% Temp. °F (°C) Resistance +/-2%
-40 (-40) 335,671 40 (4.4) 26,106 90 (32.2) 7,332
-20 (-28.9) 164,959 50 (10) 19,904 100 (37.8) 5,826
0 (-17.8) 85,323 60 (15.6) 15,313 120 (48.9) 3,756
20 (-6.7) 46,218 70 (21.1) 11,884 130 (54.4) 3,047
30 (-1.1) 34,566 80 (26.7) 9,298
4.2. Optional Room Sensor
Room sensor (A2) is a two-wire thermistor with 1k series resistor.
Temp. °F (°C) Resistance +/-2% Temperature °F
(°C)
Resistance +/-2% Temp. °F (°C) Resistance +/-2%
40 (4.4) 27,102 60 (15.6) 16,313 80 (26.7) 10,299
45 (7.2) 23,764 65 (18.3) 14,474 85 (29.4) 9,249
50 (10) 20,898 70 (21.1) 12,882 90 (32.2) 7,529
55 (12.8) 18,433 75 (23.9) 11,498
4.3. Optional Relative Humidity Sensor
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.
4.4. Optional Carbon Dioxide (Indoor Air Quality) 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
PPM
DC Voltage Carbon
Dioxide PPM
DC Voltage Carbon
Dioxide PPM
DC Voltage Carbon
Dioxide PPM
DC Voltage
0 0 600 3 1200 6 1800 9
200 1 800 4 1400 7 2000 10
400 2 1000 5 1600 8
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