Service manual

A DJM3.2 MANUAL
BMS RESET FROM VOLTAGE APPLIED TO + AND Β
Current Reset Voltage
(MA) (VDC)
Calculated Set-Point
ºC ºF
0
13 55
3 3
13.5 56
5 4
14.5 58
12 6
16 61
7
18 65
16 8
20 68
9
23 75
20 10
26 79
BMS Calibration
1. Apply 100% ma or voltage signal to the DJM3.2 “+” and “Β” terminals (i.e. 10 VDC or 20 ma).
2. Record the settings of dipswitches 1, 2, and 3. Turn off dipswitches 1, 2, and 3.
3. Measure the DJM3.2 calculated set-point. (DC voltage across resistor R124.)
4. Turn dipswitch 1 on.
5. Measure the DJM3.2 calculated set-point DC voltage again and adjust Pot BMS Cal (located next
to terminal Z) until the voltage is equal to the number of ºC maximum reset.
6. Return the dipswitches to their normal position.
Ambient Reset (continuous blower operation only)
This option requires an ambient sensor (Johnson TE 6000-960) wired to terminals X and Z. The
discharge air set-point will be reset upwards based on the ambient temperature. Ambient
temperatures below 70ºF will gradually increase the calculated discharge air set-point. The maximum
increase in the discharge temperature will be reached when the ambient falls to 20ºF. The amount of
reset is dependant on the position of Pot Reset Ratio and the discharge set-point as set on the dial.
(The discharge set-point will be reset below master set-point if ambient is above 70ºF. In most cases when the
outside ambient is above 70ºF, the heat will be off.)
It is possible to obtain an extended temperature range by placing a 120-ohm resistor in series with the
ambient temperature sensor.
NOTE: With this resistor the discharge temperature will be at its maximum when ambient
is at -15ºF.
Be aware with this resistor, the calculated discharge air set-point equals the dial set-point at 35ºF
(different from above). Above 40ºF the calculated discharge air temperature will be below the dial set-
point. Note the sample on the following graph.
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Modified Reset
**
Slope with 120 ohm Resistor
Standard Reset Slope
80°F
60°F 40°F
-20°F 0°F
Horizontal Axis is Ambient Temperature Scale
Vertical Axis is Dial Set-Point Line
(Adjustable 0-35°C)
20°F
The above graph shows the “Standard Reset Slope” if an outdoor ambient reset sensor is activated.
As the outdoor temperatures cool down, the discharge temperature is driven higher until at about
Page 16 Revised: 3/11/99