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Compressor Safety (standalone mode)
Compressor Safety may be configured on Binary Input 3. This
feedback can be provided by a compressor.
Lock-Out (CLO) device or current switch when field installed. A
Compressor Safety Alarm indicates that the equipment requires
attention. Cooling, heating, and supply fan outputs are not
interrupted. Normal operation resumes when the compressor safe-
ty circuit is de-energized.
Fan Status (standalone mode)
Fan Status may be configured on any unused binary input channel.
A typical application would be an airflow switch, current sensing
relay, or other device that provides a supply fan running verifica-
tion. Enabling this function displays the supply fan's status on the
equipment graphic. If the controller loses fan status during opera-
tion, heating and cooling are disabled, the economizer damper (if
available) is closed, and an alarm for loss of status is indicated. If
the fan status is on when the controller is commanding the fan off,
the unit remains in the off state. An alarm is generated indicating
that the fan is running when it should be off.
Filter Status (standalone mode)
Filter status may be configured on any unused binary input chan-
nel. A typical application is a differential pressure switch that
senses the pressure drop across a filter bank. When the pressure
across the filter bank exceeds the setpoint of the differential pres-
sure switch, the Filter status is displayed as Dirty on the controller
graphic. An alarm indicates a dirty filter.
TROUBLESHOOTING
General
The VAV-RTU Open controller acts as an intelligent imbedded
thermostat to the rooftop unit, but can be monitored and controlled
from i-Vu Open (Linkage) or a third 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 con-
troller, 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 VAV-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 (see Fig. 2). It is a 3-volt lithium battery (CR2032). The aver-
age life is 7 years with a minimum of 10,000 hours of back-up.
When the VAV-RTU Open board is powered up, the battery is not
being used. If power is lost, the battery backs up the time clock.
REPLACING THE VAV-RTU OPEN BATTERY
To determine when to replace the battery, remove and measure the
voltage. If the voltage is below 2.9 volts, replace the battery.
CAUTION
UNIT OPERATION HAZARD
Power must be ON to the VAV-RTU Open when replacing the
battery or date, time, and trend data will be lost.
1.
Remove the battery from the controller, making note of the
battery's polarity.
2.
Insert the new battery, matching the battery's polarity with the
polarity indicated on the VAV-RTU Open .
Thermistor Troubleshooting
VAV-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 on
page 6. Thermistors are used for supply air temperature (SAT), re-
turn air temperature (RAT) and outdoor air temperature (OAT).
To check accuracy, use a high quality digital volt-ohmmeter.
Connect the meter to the thermistor leads to obtain a resistance
value. Use Table 2 to convert that resistance to a temperature. The
next step is to measure temperature at probe location with an
accurate thermocouple-type temperature-measuring instrument.
Temperature measured by thermocouple and temperature deter-
mined 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 VAV-RTU Open's calibration
function to offset the temperature reading.
Table 2 — Thermistor Resistance vs Temperature
Values for Space Temperature Sensor, Supply Air
Temperature Sensor, and Outdoor Air Temperature
TEMP (C)
TEMP (F)
–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 VAV-RTU Open's software version. To do
this a module status (Modstat) must be run on the controller. This
can be done from Field Assistant or from Equipment or System
Touch. An example of the beginning lines of a Modstat is shown
in Fig. 20. The application software version shows the current run-
ning
software
of
vav_rtu_open_20180828 refers to VAV-RTU Open software ver-
sion 20180828. The last 8 digits of the number refer to a date
(YYYYMMDD). The first 4 digits are the year (2018) and the
month and day (0828), so this version is August 28, 2018.
29
Sensor
RESISTANCE (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
the
board.
In
this
case
the
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