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FORM 150.72-NM3 (1020)
ISSUE DATE 10/05/2020
CHECKING INPUTS AND OUTPUTS
Digital Inputs
Refer to the unit wiring diagram. All digital inputs are
connected to J13-1 of the I/O board. The term "digital"
refers to two states – either on or off. As an example,
when the flow switch is closed, 30VDC will be applied
to J13, pin 5 (J13-5) of the I/O board. If the flow switch
is open, 0VDC will then be present at J13-5.
Pin 1 of J13 is an unregulated 30VDC source used to
supply the DC voltage to the various user contacts, unit
switch, flow switch, etc. This DC source is factory wired
to XTBC1, terminal 13. Any switch or contact used as a
digital input would be connected to this terminal, with
the other end connecting to its respective digital input on
the microboard. Any time a switch or contact is closed,
30VDC would be applied to that particular digital input.
Any time a switch or contact is open, 0VDC would be
applied to that particular digital input.
Typically, voltages of 24 – 36VDC could be measured
for the DC voltage on the digital inputs. This voltage
is in reference to ground. The unit case should be
sufficient as a reference point when measuring digital
input voltages.
Analog Inputs – Temperature
Refer to the unit wiring diagram. Temperature inputs are
connected to the microboard on plug J6. These analog
inputs represent varying DC signals corresponding to
varying temperatures. All voltages are in reference to
the unit case (ground). Following are the connections
for the temperature sensing inputs:
Outside Air Sensor
J6-6 = +5VDC regulated supply to sensor.
J6-9 = VDC input signal to the microboard.
See Table 24 for voltage readings that corre-
spond to specific outdoor temperatures.
J6-3 = drain (shield connection = 0VDC) Return
JOHNSON CONTROLS
SECTION 9 – SERVICE AND TROUBLESHOOTING
TABLE 24 – OUTDOOR AIR SENSOR
TEMPERATURE/VOLTAGE/
CORRELATION
VOLTAGE
TEMP °F
(Signal Input
to Return)
0
0.7
5
0.8
10
0.9
15
1.0
20
1.1
25
1.2
30
1.4
35
1.5
40
1.7
45
1.8
50
2.0
55
2.2
60
2.3
65
2.5
70
2.6
75
2.8
80
2.9
85
3.1
90
3.2
95
3.4
100
3.5
105
3.6
110
3.7
115
3.8
120
3.9
125
4.0
130
4.1
TEMP °C
-18
-15
-12
-9
-7
-4
-1
2
4
7
10
13
16
18
21
24
27
29
32
35
38
41
43
46
49
52
54
9
181
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