Fan Status; Filter Status; Door Switch; Remote Occupancy - Carrier 48/50HC04-28 Controls, Start-Up, Operation And Troubleshooting

Fan Status

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 verification. Enabling this function displays the
supply fan's status on the equipment graphic. If the
controller loses fan status during operation, 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

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 differential 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
input. 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 immediate 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, controlled by a third party, or an occupancy
sensor to set the controller's occupied mode. The Remote
Occupancy function requires 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 unoccupied mode, as
determined by the state of the Remote Occupancy input.

Linkage

The RTU Open may serve as an air source to an Open
Variable Volume and Temperature (VVT
the RTU Open is part of a VVT system and the controllers
are wired together to form a network, the controllers may
use a method of communication known as Linkage. Linkage
is a method by which an air source and its subordinate zone
terminals exchange data to form a coordinated HVAC
system. The system's air source controller, zone controllers,
and bypass controller are linked so that their data exchange
can be managed by one zone controller configured as the
VVT Master. The VVT Master gathers the following
information from the slave zone controllers:
S occupancy status
S setpoints
S zone temperature
S relative humidity
S CO level
2
S damper position
S optimal start data
The VVT Master performs mathematical calculations and
algorithms on the data and then sends the composite
information 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:
S Off – Air source fan is off
S Fan Only – Air source fan is on and providing
ventilation (neutral SAT) without heating or cooling
S Economizer Cooling – Air source fan is on and
providing cooling, using economizer only
S Cooling – Air source fan is on and cooling is provided
by economizer and mechanical cooling
S Heating – Air source fan is on and heating is provided
(gas or electric)
S Dehumidification – Air source fan is on and
Humidi- - MiZer
S Test – The RTU Open Service Test mode is active
S Shutdown – Air source fan is off due to Safety Chain,
Fire Shutdown, or invalid SAT sensor
S Unocc Free Cooling – Air source fan is on, with the
economizer providing cooling while unoccupied

General

The 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 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,
R
) system. When
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 (see Fig. 1). 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.

Replacing the RTU Open's Battery

To determine when to replace the battery, remove and
measure the voltage. If the voltage is below 2.9 volts,
replace the battery.
25
R
is active

TROUBLESHOOTING