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Form 150.72-ICOM6
Issue date: 12/19/2023
Checking inputs and outputs
Digital inputs
See the unit wiring diagram. All digital inputs are con-
nected 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, 30 VDC will be ap-
plied to J13, pin 5 (J13-5) of the I/O board. If the flow
switch is open, 0 VDC 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 XTBC1, Terminal 13. Any switch or contact
used as a digital input would be connected to this ter-
minal, with the other end connecting to its respective
digital input on the microboard. Any time a switch or
contact is closed, 30 VDC would be applied to that par-
ticular digital input. Any time a switch or contact is
open, 0 VDC would be applied to that particular digital
input.
Typically, voltages of 24 VDC to 36 VDC 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 digi-
tal input voltages.
Analog inputs, temperature
See 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
See Table 31 on page 189 for voltage readings
that correspond to specific outdoor tempera-
tures.
J6-3 = drain (shield connection = 0 VDC) return
Johnson Controls
to
the
microboard.
Section 9: Service and troubleshooting
Table 31: 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
189
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Table of Contents
Troubleshooting
