JOHNSON CONTROLS
165
SECTION 9 – SERVICE AND TROUBLESHOOTING
FORM 150.72-ICOM6
ISSUE DATE: 12/29/2017
9
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, 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 ter-
minal, 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 par-
ticular digital input. Any time a switch or contact is
open, 0VDC would be applied to that particular digital
input.
Typically, voltages of 24 to 36VDC could be measured
for the DC voltage on the digital inputs. This voltage is
in reference to ground. The unit case should be suffi-
cient as a reference point when measuring digital 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 = +5VDC regulated supply to sensor.
J6-9 = VDC input signal to the microboard.
See Table 29 on page 165 for voltage readings
that correspond to specific outdoor tempera-
tures.
J6-3 = drain (shield connection = 0VDC) return
TABLE 29 - OUTDOOR AIR SENSOR
TEMPERATURE/VOLTAGE/
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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