Filter Status; Door Switch; Remote Occupancy; Linkage - Carrier RTU Open Controls, Start-Up, Operation And Troubleshooting

Filter Status

Filter status may be configured on any unused binary input
channel. 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 dif-
ferential pressure switch, the Filter status is displayed as Dirty
on the controller graphic. An alarm indicates a dirty filter.

Door Switch

A Door Contact may be configured on any unused binary in-
put. A typical application is an occupancy sensor mounted
within the space served by a single zone rooftop. Door Contact
disables mechanical cooling and electric or gas heating, when
active. Economizer cooling, if available, continues to operate.
A configurable Door Alarm Delay is provided to prevent im-
mediate action. The default is set to 60 seconds.

Remote Occupancy

Remote occupancy may be configured on any unused binary
input channel. A typical application is a remote contact, con-
trolled by a third party, or an occupancy sensor to set the con-
troller's occupied mode. The Remote Occupancy function re-
quires both an input configured for Remote Occupancy, and
Occupancy Source set to Remote Occ Input to operate. Once
configured, the controller will operate in the occupied or unoc-
cupied mode, as determined by the state of the Remote Occu-
pancy input.

Linkage

The RTU Open controller may serve as an air source to an
Open Variable Volume and Temperature (VVT
When the RTU Open controller is part of a VVT system and
the controllers are wired together to form a network, the con-
trollers may use a method of communication known as Link-
age. Linkage is a method by which an air source and its subor-
dinate zone terminals exchange data to form a coordinated
HVAC system. The system's air source controller, zone con-
trollers, and bypass controller are linked so that their data ex-
change can be managed by one zone controller configured as
the VVT Master. The VVT Master gathers the following infor-
mation from the slave zone controllers:
• occupancy status
• setpoints
• zone temperature
• relative humidity
• CO level
2
• damper position
• optimal start data
The VVT Master performs mathematical calculations and
algorithms on the data and then sends the composite informa-
tion to the air source. The VVT Master receives information
from the air source such as mode, supply air temperature, and
outside air temperature, and passes that information to all
linked controllers.

LINKAGE AIR SOURCE MODES

In a linked system, the air source determines its operating
mode and qualifies that mode based on its own Supply Air
Temperature (SAT). The following modes can be sent by the
air source depending on its configuration:
• Off – Air source fan is off
• Fan Only – Air source fan is on and providing ventilation
(neutral SAT) without heating or cooling
• Economizer Cooling – Air source fan is on and providing
cooling, using economizer only
• Cooling – Air source fan is on and cooling is provided by
economizer and mechanical cooling
• Heating – Air source fan is on and heating is provided (gas
or electric)
• Dehumidification – Air source fan is on and Humidi-MiZer
is active
• Test – The RTU Open Service Test mode is active
• Shutdown – Air source fan is off due to Safety Chain, Fire
Shutdown, or invalid SAT sensor
• Unocc Free Cooling – Air source fan is on, with the econo-
mizer providing cooling while unoccupied

General

The RTU Open controller acts as an intelligent embedded ther-
mostat to the rooftop unit, but can be monitored and controlled
from i-Vu
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 controller 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. 1). It is a 3-volt lithium battery (CR2032). The aver-
) system.
®
age 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.
REPLACING THE RTU OPEN CONTROLLER BATTERY
To determine when to replace the battery, remove and measure the
voltage. If the voltage is below 2.9 volts, replace the battery.
UNIT OPERATION HAZARD
Power must be ON to the RTU Open controller 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 RTU Open controller.

Thermistor Troubleshooting

The RTU Open controller uses thermistors to sense tempera-
tures 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 tem-
perature (SAT), outdoor air temperature (OAT), and space tem-
perature (SPT) and all must be a 10 kilo-ohm type II sensor.
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.
Next step is to measure temperature at probe location with an ac-
curate 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 read-
ings. If a sensor must be corrected, use the RTU Open controller
calibration function to offset the temperature reading.
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TROUBLESHOOTING

® Open (Linkage) or a 3rd party network. This causes
CAUTION
®