FORM 150.66-NM2
ISSUE DATE: 09/25/2020
147
JOHNSON CONTROLS
SECTION 9 - SERVICE AND TROUBlEShOOTING
9
CHECKING INPUTS AND OUTPUTS
Digital Inputs
Refer to the unit wiring diagram.
All digital inputs are
connected to J13 of the microboard. The term “digital”
refers to two states – either on or off. As an example,
when the flow switch is closed, 30 volts
DC
will be
applied to J13, pin 5 (J13-5) of the microboard. If the
flow switch is open, 0 volts DC will then be present at
J13-5.
Pin 1 of J13 is an
unregulated
30 VDC
source
used to
supply the DC voltage to the various user contacts, unit
switch, flow switch, etc. This
DC source is factory wired
to CTB1, 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 as high as 34 VDC could be mea-
sured 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 = +5 VDC regulated supply to sensor.
J6-9 = VDC input signal to the microboard.
See Table 28 for voltage readings that corre
spond to specific outdoor temperatures.
J6-3 = drain (shield connection = 0VDC) Return
TABLE 28 – OUTDOOR AIR SENSOR
TEMPERATURE/VOLTAGE/RESISTANCE
CORRELATION
TEMP°F
VOlTAGE
(Signal Input
to Return)
TEMP°C
0
0.7
-18
5
0.8
-15
10
0.9
-12
15
1.0
-9
20
1.1
-7
25
1.2
-4
30
1.4
-1
35
1.5
2
40
1.7
4
45
1.8
7
50
2.0
10
55
2.2
13
60
2.3
16
65
2.5
18
70
2.6
21
75
2.8
24
80
2.9
27
85
3.1
29
90
3.2
32
95
3.4
35
100
3.5
38
105
3.6
41
110
3.7
43
115
3.8
46
120
3.9
49
125
4.0
52
130
4.1
54
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