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VIII--Multi-Staged Blower
NOTE - VFD Bypass is only offered in LDT156,180 models.
A-Design Specifications
Use the “Blower CFM Design Specifications” table
attached to the unit (table 18 in the installation instructions)
to fill in test and balance values when setting up the unit.
If only high and low cooling design specifications are
provided, set the medium cooling CFM at the high or low
cooling design spec or any CFM between.
B-Set Maximum CFM
Use attached table to determine highest blower CFM for
appropriate unit. Adjust the blower pulley to deliver that
amount of CFM with only the blower operating. See
Determining Unit CFM in the Blower Operation and
Adjustment section.
C-Set Blower Speeds
1- Use the following mobile service app menu to enter the
blower design specified CFM into the Unit Controller.
Make sure blower CFM is within limitations shown in
table 15 or 16 . Refer to the Unit Controller manual
provided with unit.
RTU MENU > RTU OPTIONS > BLOWER > SPEED
2- Enter the following design specifications as shown in
the attached table (table18 in the installation
instructions).
Blower / Heating High CFM
Cooling High CFM
Cooling Low CFM
Vent CFM
3- Adjust the blower RPM to deliver the target CFM based
on the measured static pressure using the blower
table.
4- Measure the static pressure again and apply the static
pressure and RPM to the blower tables to determine
adjusted CFM.
5- Repeat adjustments until design CFM is reached.
D-Set Damper Minimum Position
To maintain required minimum ventilation air volumes
when the unit is in the occupied mode, two minimum
damper positions must be set.
The Unit Controller will open the damper to “Min OCP Blwr
High” when blower CFM is at or ABOVE the “midpoint”
CFM.
The Unit Controller will open the dampers to “Min OCP
Blwr Low” when blower CFM is BELOW a “midpoint”
CFM.
The Unit Controller will calculate the “midpoint” CFM.
*Available blower speeds vary by unit and thermostat
stages.
Set Minimum Position 1
Use the following mobile service app menu to set “Min OCP
Blwr High” for the blower CFM above the “midpoint” CFM.
When navigating into this menu, the Unit Controller will run
damper calibration and allow damper position adjustment.
RTU MENU > SETTINGS > RTU OPTIONS > DAMPER
Tap "Next" to skip tabs and complete damper position
calibration until "Damper Calibration Blower Speed High"
tab appears.
Measure the intake air CFM. If the CFM is lower than the
design specified CFM for ventilation air, use the Unit
Controller to increase the damper percent open. If the CFM
is higher than specified, decrease the damper percent
open.
Note - Intake air CFM can also be determined using the
outdoor air temperature, return air temperature and mixed
air temperature. Refer to the economizer or outdoor air
damper installation instructions.
Set Minimum Position 2
Use the following mobile service app menu in the Unit
Controller to set “Min OCP Blwr Low” for the blower CFM
below the “midpoint” CFM. When navigating into this menu,
the Unit Controller will run damper calibration and allow
damper position adjustment.
RTU MENU > SETTINGS > RTU OPTIONS > DAMPER
Tap "Next" to skip tabs and complete damper position
calibration until "Damper Calibration Blower Speed High"
tab appears.
Measure the intake air CFM. If the CFM is lower than the
design specified CFM for ventilation air, use the Unit
Controller to increase the damper percent open. If the CFM
is higher than specified, decrease the damper percent
open.
Note - Intake air CFM can also be determined using the
outdoor air temperature, return air temperature and mixed
air temperature. Refer to the economizer or outdoor air
damper installation instructions.
E-Inverter Bypass Option
The supply air inverter is factory-set to by-pass the inverter
manually. To by-pass the inverter and operate the blower in
the constant air volume mode, use the following Unit
Controller menu and set to “engaged”:
SETTINGS > RTU OPTIONS > BLOWER > VFD
BYPASS
To configure the unit to by-pass the inverter automatically,
use the following Unit Controller menu.
SETUP > INSTALL
Press SAVE until the menu reads:
CONFIGURATION ID 1
Change the 6
th
character position to A for automatic bypass
option.
Press SAVE
Caution - Units not equipped with an inverter will have the
6
th
character set to N, indicating the inverter is not
bypassed. The blower motor could be damaged and/or
result in product or property damage if the setting is
changed to automatic or manual.
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