Variable Air Volume Start-Up - Lennox LGH480 Installation Instructions Manual

Variable Air Volume Start-Up

Units may contain an optional supply air blower equipped
with a variable frequency drive A96 (VFD) which varies
supply air CFM.
The supply air VFD (A96) is located near the compressors.
See figure 22.
A-Start-Up
1- A pressure transducer (A30) is shipped in a box in the
blower compartment. Install the transducer according
to manufacturer's instructions.
Note - Make sure the transducer is installed in the main duct
at least 2/3 of the distance away from the unit.
2- Two twisted pairs of shielded cable must be used to
connect the pressure transducer. See figure 23.
3- Open all zone dampers and/or boxes.
4- Locate the A55 Unit Controller in the control box.
5- Use the Unit Controller to calibrate the blower CFM.
Select the SETUP->TEST & BALANCE->BLOWER
menu to start the blower. The Unit Controller will
display the percent of blower speed. Adjust blower
speed percentage
specifications. Allow blower speed to stabilize.
6- Press SAVE to display the current static pressure. If
the static pressure meets the design specification,
press SAVE again to set the setpoint. If the static
pressure does not meet the design specification,
adjust the pressure and press SAVE to set the
setpoint.
7- Record new setpoints in table 4.
Note - The Unit Controller will lock-out the unit for 5
minutes if static pressure exceeds 2.0"w.c. for 20
seconds. The Unit Controller will permanently shut down
the unit after three occurrences. See Unit Controller
parameters 110, 42, and 43 to adjust default values.
8- If the desired CFM cannot be met with current pulley
setup, refer to the Blower Operation and Adjustments
section to adjust CFM.
B-Unit Operation
Use the Unit Controller to check unit mechanical operation.
See the Service - Test section of the Unit Controller manual.
C-Supply Air VFD By-Pass Plug (Optional)
IMPORTANT - All dampers must be open to prevent
damage to duct work and dampers.
TABLE 4
RECORD ADJUSTED SETPOINTS
Setpoint
Parameter
Description
386 Smoke
387 Ventilation
388 Heating
389 Cooling
to meet design airflow
Setpoint Display
"w.c. Setting
The supply air VFD may be by-passed using jack/plug
connections. Locate J/P198 connectors in control box
area under the relays. Disconnect J198 from P198 and
connect J204 to P198. See figure 24. Blower will operate in
constant air volume mode.
SUPPLY AIR VARIABLE FREQUENCY DRIVE
OPTIONAL
VIEW SHOWN
FROM FRONT
SIDE OF UNIT
PRESSURE TRANSDUCER WIRING
A30
+
NOT
_
CONNECTED
NOT
CONNECTED
+
SUPPLY AIR VFD BY-PASS CONNECTOR
CONNECTORS USED
FOR SUPPLY AIR
VFD OPERATION
J198
P198
Page 18
SUPPLY AIR
VFD (A96)
OUTDOOR
AIR
SECTION
A34
FIGURE 22
CONTROLLER
TWISTED
PAIR
DRAIN
TWISTED
PAIR
UNUSED WIRE
FIGURE 23
CONNECTORS USED TO BY-PASS
VFD AND OPERATE SUPPLY AIR
BLOWER AT MAXIMUM SPEED
J204
P198
FIGURE 24
LGH/LCH420, 480, 540, 600
UNIT
TB18
6
9
TB24
26