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QUANTECH
145
SECTION 9 – SERVICE AND TROUBLESHOOTING
Form QCC2-NM1
Issue Date: 5/20/2021
9
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, 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 – 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 suffi-
cient 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
an-
alog
inputs represent varying DC signals correspond-
ing to varying temperatures. All voltages are in refer-
ence to the unit case (ground). The 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
correspond to specific outdoor temperatures.
J6-3 = drain (shield connection = 0 VDC) Return
Table 27 -
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
Table 28 -
Discharge Air Temp. Sensor Temperature/
Содержание QCC2015CEE
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