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Fan Status Monitoring
GENERAL — The A Series ComfortLink controls offer the ca-
pability to detect a failed supply fan through either a duct static
pressure transducer or an accessory discrete switch. The fan sta-
tus switch is an accessory that allows for the monitoring of a dis-
crete switch, which trips above a differential pressure drop across
the supply fan. For any unit with a factory-installed duct static
pressure sensor, it is possible to measure duct pressure rise di-
rectly, which removes the need for a differential switch. All
48/50A3,A5 units with a factory-installed supply fan VFD will
have the duct static pressure sensor as standard.
SETTING UP THE SYSTEM — The fan status monitoring
configurations are located in Configuration
Table 62.
Table 62 — Fan Status Monitoring Configuration
ITEM
EXPANSION
SFS.S
Fan Fail Shuts Down Unit Yes/No
SFS.M
Fan Stat Monitoring Type 0 - 2
Fan Stat Monitoring Type (SFS.M) — This configuration se-
lects the type of fan status monitoring to be performed.
0 - NONE — No switch or monitoring
1 - SWITCH — Use of the fan status switch
2 - SP RISE — Monitoring of the supply duct pressure.
Fan Fail Shuts Down Unit (SFS.S) — This configuration
will configure the unit to shut down on a supply fan status fail
or simply alert the condition and continue to run. When config-
ured to YES, the control will shut down the unit if supply fan
status monitoring fails and the control will also send out an
alarm. If set to NO, the control will not shut down the unit if
supply fan status monitoring fails but will send out an alert.
SUPPLY FAN STATUS MONITORING LOGIC — Regard-
less of whether the user is monitoring a discrete switch or is
monitoring static pressure, the timing for both methods is the
same and rely upon the configuration of static pressure control.
The configuration that determines static pressure control is Con-
figuration
SP
SP.CF. If this configuration is set to 0 (none),
a fan failure condition must wait 60 continuous seconds before
taking action. If this configuration is 1 (VFD), a fan failure con-
dition must wait 3 continuous minutes before taking action.
If the unit is configured to monitor a fan status switch
(SFS.M = 1), and if the supply fan commanded state does not
match the supply fan status switch for 3 continuous minutes,
then a fan status failure has occurred.
If the unit is configured for supply duct pressure monitoring
(SFS.M = 2), then
• If the supply fan is requested ON and the static pressure
reading is not greater than 0.2 in. wg for 3 continuous
minutes, a fan failure has occurred.
• If the supply fan is requested OFF and the static pressure
reading is not less than 0.2 in. wg for 3 continuous min-
utes, a fan failure has occurred.
Dirty Filter Switch —
field-installed accessory dirty filter switch. The switch is located
in the filter section. If a dirty filter switch is not installed, the
switch input is configured to read "clean" all the time.
To enable the sensor for dirty filter monitoring set
Configuration
UNIT
SENS
state of the filter status switch can be read at Inputs
FLT.S. See Table 63.
Table 63 — Dirty Filter Switch Points
ITEM
EXPANSION
Configuration
UNIT
Filter
SENS
FLT.S
Stat.Sw.Enabled ?
Inputs
GEN.I
Filter Status Input DRTY/CLN FLTS
FLT.S
UNIT. See
RANGE
CCN POINT
SFS_SHUT
SFS_MON
The unit can be equipped with a
FLT.S to ENABLE. The
GEN.I
CCN
RANGE
POINT
Enable/
FLTS_ENA
Disable
Monitoring of the filter status switch is disabled in the
Service Test mode and when the supply fan is not commanded
on. If the fan is on and the unit is not in a test mode and the
filter status switch reads "dirty" for 2 continuous minutes, an
alert is generated. Recovery from this alert is done through a
clearing of all alarms or after cleaning the filter and the switch
reads "clean" for 30 seconds.
NOTE: The filter switch should be adjusted to allow for the
operating cfm and the type of filter. Refer to the accessory
installation instructions for information on adjusting the switch.
Economizer —
the outside and return air dampers of the unit to provide venti-
lation air as well as free cooling based on several configuration
options. This section contains a description of the economizer
and its ability to provide free cooling. See the section on Indoor
Air Quality Control on page 65 for more information on setting
up and using the economizer to perform demand controlled
ventilation (DCV). See the Third Party Control section on
page 25 for a description on how to take over the operation of
the economizer through external control.
The economizer system also permits this unit to perform
smoke control functions based on external control switch
inputs. Refer to the Smoke Control Modes section on page 65
for detailed discussions.
Economizer control can be based on automatic control
algorithms using unit-based setpoints and sensor inputs. This
economizer control system can also be managed through exter-
nal logic systems.
The economizer system is a factory-installed option. This
unit can also have the following devices installed to enhance
economizer control:
• Outside air humidity sensor
• Return air humidity sensor
NOTE: All these options require the controls expansion
module (CEM).
ECONOMIZER FAULT DETECTION AND DIAGNOS-
TICS (FDD) CONTROL — The Economizer Fault Detection
and Diagnostics control can be divided into two tests:
• Test for mechanically disconnected actuator
• Test for stuck/jammed actuator
Mechanically Disconnected Actuator — The test for a
mechanically disconnected actuator shall be performed by
monitoring SAT as the actuator position changes and the
damper blades modulate. As the damper opens, it is expected
SAT will drop and approach OAT when the damper is at
100%. As the damper closes, it is expected SAT will rise and
approach RAT when the damper is at 0%. The basic test shall
be as follows:
1. With supply fan running take a sample of SAT at current
actuator position.
2. Modulate actuator to new position.
3. Allow time for SAT to stabilize at new position.
4. Take sample of SAT at the new actuator position and de-
termine if the damper has opened or closed. If damper has
opened, SAT should have decreased. If damper has
closed, SAT should have increased.
5. Use current SAT and actuator position as samples for next
comparison after next actuator move.
The control shall test for a mechanically disconnected damper
if all the following conditions are true:
1. An economizer is installed.
2. The supply fan is running.
3. Conditions are good for economizing.
4. The difference between RAT and OAT is greater than
T24RATDF. It is necessary for there to be a large enough
57
The economizer control is used to manage
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