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SGH/SCH036, 060, 120, 240
MSAV
t
Unit Start-Up
Units may contain a supply air blower equipped with a
variable frequency drive A96 (VFD) which stages supply air
CFM.
The supply air VFD (A96) is located near the compressors.
See figure 34.
FIGURE 34
SUPPLY AIR VARIABLE FREQUENCY DRIVE
SUPPLY AIR VFD (A96)
SC/SG 240 LOCATION
SUPPLY AIR VFD
(A96) SC/SG120
LOCATION
A-Design Specifications
Use table 24 to fill in field-provided, design specified blower
CFM for appropriate 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 table 24 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-Enter Design Specifications Into Controller
1- Use the following menu to enter the blower design
specified CFM into the Unit Controller. Make sure
blower CFM is within limitations shown in table 25.
Refer to the Unit Controller manual provided with unit.
SETUP>TEST & BALANCE>BLOWER> (enter information
as prompted by the Unit Controller if not already done).
2- Enter the following design specifications as shown in
table 30.
Blower /
Heat CFM
Cooling High CFM
1
Cooling Low CFM
1
Vent CFM
1
The Unit Controller will prompt when more cooling stages
are available depending on the number of compressors and
the control mode.
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 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
dampers to “Min OCP Blwr Low” when blower CFM is
BELOW a “midpoint” CFM. 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 calculate the “midpoint” CFM.
Set Minimum Position 1
Use the following 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 bring on the corresponding blower speed and allow
damper position adjustment.
SETTINGS>RTU OPTIONS>DAMPER>
MIN DAMPER POSITION BLOWR ON HIGH = X.X%
TABLE 24
Blower CFM Design Specifications
Unit
T'Stat or
Zone Con
trol Stages
Blower Speed
Design
Specified CFM
120,
240
2
Htg.
Clg. High
Clg. Low
Ventilation
240
4
Htg.
Clg. High
Clg. Med. High
Clg. Med. Low
Clg. Low
Ventilation
*Available blower speeds vary by unit and thermostat
stages.
