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TROUBLESHOOTING
General
The RTU Open controller acts as an intelligent imbedded
thermostat to the rooftop unit, but can be monitored and
controlled from a 3rd party network. This causes the
system as a whole to be troubleshot from three points of
view. The three parts to the system are the rooftop unit,
the Open controller, and the network connected.
Determining which part needs to be troubleshot is the first
step.
The Open controller can be used to troubleshoot the
rooftop unit and/or itself with service test, communicating
LED's, and built in alarms. Disconnecting the RTU Open
from the network may also help troubleshooting the
controller and rooftop unit. Third Party Network
troubleshooting may also be required. For base unit
troubleshooting, refer to specific base unit Service
Maintenance manual.
There is an on- board battery that is used for RAM and
clock back- up. It is a 3- volt lithium battery (CR2032).
The average life is 7 years with a minimum of 10,000
hours of back- up. When the RTU Open board is powered
up, the battery is not being used. If power is lost, the
battery backs up the time clock. Battery replacement
should be done with the board powered up.
Thermistor Troubleshooting
RTU Open uses thermistors to sense temperatures for
control operation of the unit. Resistances at various
temperatures are listed in Table 2. Thermistor pin
connections are shown in Table 1. Thermistors are used
for supply air temperature (SAT), outdoor air temperature
(OAT), and space temperature (SPT) and all must be a 10
kilo-ohm type II sensor.
To
check
accuracy,
use
volt-ohmmeter. Connect the meter to the thermistor leads
to obtain a resistance value. Use Table 2 to convert that
resistance to a temperature. Next step is to measure
temperature
at
probe
thermocouple-type
temperature-measuring
Temperature measured by thermocouple and temperature
determined from thermistor voltage reading should be
close, within 5_F if care was taken in applying
thermocouple and taking readings. If a sensor must be
corrected, use the RTU Open's calibration function to
offset the temperature reading.
a
high
quality
digital
location
with
an
accurate
instrument.
Table 2 – Thermistor Resistance vs Temperature Values
for Space Temperature Sensor, Supply Air Temperature
Sensor, and Outdoor Air Temperature Sensor
TEMP
TEMP
(C)
- 40
- 35
- 30
- 25
- 20
- 15
- 10
- 5
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Software Version
During Start-up and throughout the life of the equipment,
it may be necessary to obtain the RTU Open's software
version. To do this a Modstat must be run on the
controller. This can be done from the BACview user
interface by holding the function (FN) key and pressing
the period (.) key. An example of the beginning lines of a
Modstat is shown in Fig. 16. The application software
version shows the current running software of the board.
In this case the rtu_open-20100409 refers to RTU Open
software version 20100409. This 8 digit number refers to
a date (YYYYMMDD). The first 4 digits are the year
(2010) and the month and day (0409), so this version is
th
April 9
2010.
21
RESISTANCE
(F)
(Ohms)
- 40
335,651
- 31
242,195
- 22
176,683
- 13
130,243
- 4
96,974
5
72,895
14
55,298
23
42,315
32
32,651
41
25,395
50
19,903
59
15,714
68
12,494
77
10,000
86
8,056
95
6,530
104
5,325
113
4,367
122
3,601
131
2,985
140
2,487
149
2,082
158
1,752
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