Sequence of Operation
62 RT-SVX21AC-EN
operating in heating mode the heat speed set
cannot be lower than Speed Set 4.
4. To stop the SERVICE TEST, turn the
main power
disconnect switch to the “Off” positi
on or proceed to
the next component start-up procedure.
Units with Belt Drive Indoor Fan
Much of the systems performance and reliability is closely
associated with, and dependent upon having the proper
airflow supplied both to the space that is being
conditioned and across the evaporator coil.
The indoor fan speed is changed by opening or closing the
ad
justable motor
sheave.
Before starting the SERVICE TES
T, set the minimum
position setpoint for
the economizer to 0 percent using the
setpoint potentiometer located on the Economizer Control
(ECA), if applicable.
ReliaTel™ Control: Using the Service Test Guide in
Table 16, p. 51, momentarily jump across the Test 1 and
Test 2 terminals on LTB1 one time to start the Minimum
Ventilation Test.
Electromechanical Control: Using the Service Test
Guide perform the proper test mode connections.Once the
supply fan has started, check for proper rotation. The
direction of rotation is indicated by an arrow on the fan
housing.
With the fan operating properly, determine the total
system
airflow (CFM) b
y (ReliaTel™/Electromechanical):
1. Measuring the actual RPM,
2. Measure the amperage at the supply fan contactor and
com
pare it with
the full load amp (FLA) rating stamped
on the motor nameplate.
a. Calculate the theoretical BHP using (Actual Motor
Am
ps/ Mo
tor Nameplate Amps) X Motor HP.
b. Using the fan performance tables in the unit Service
Facts, plot
the actual RPM (step 1) and the BHP (step
2a) to obtain the operating CFM.
3. If the required CFM is too low, (external static pressure
i
s high
causing motor HP output to be below table
value),
a. Relieve supply and/or return duct static.
b. Change indoor fan speed and repeat steps 1 and 2.
• To Increase Fan RPM; Loosen the pulley adjustment
set
screw a
nd turn sheave clockwise.
• To Decrease Fan RPM; Loosen the pulley adjustment
set screw a
nd turn sheave counterclockwise.
• If the required CFM is too high, (external static
pressu
re is low causing motor HP output to be above
table value), change indoor fan speed and repeat steps
1 and 2.
• To stop the SERVICE TEST, turn the m
ain power
disconnect switch to the “Off” position or proceed to
the next component start-up procedure.
Units with Direct Drive Indoor Fan -
Electromechanical Control
Much of the systems performance and reliability is closely
associated with, and dependent upon having the proper
airflow supplied both to the space that is being
conditioned and across the evaporator coil. The indoor fan
speed is changed by adjusting the output voltage from the
MMC/ECM board to the direct drive fan. Before starting the
SERVICE TEST, set the minimum position setpoint for the
economizer to 0 percent using the setpoint potentiometer
located on the Economizer Control (ECA), if applicable.
ReliaTel™ Units with Direct Drive Indoor
Fan
Note: 10 tons standard efficiency, 6 (074) to 10 tons high
efficiency and optional on 7.5 (092) to 8.5 tons
standard efficiency
Much of the systems performance and reliability is closely
associate
d with, and dependent upon having the proper
airflow supplied both to the space that is being
conditioned and across the evaporator coil. The indoor fan
speed is changed by adjusting the voltage from the RTOM
indoor fan speed output to the direct drive plenum fan. If
installed, before starting the SERVICE TEST disable the
economizer by disconnecting the 4 pin power connector
located at the base of the Economizer Control (ECA).
Using the service test guide in Table 16, p. 51,
m
ome
ntarily jump across the Test 1 and Test 2 terminals
on LTB1. Repeat process until Service Test Mode is at Cool
2 (2-Steps of Cooling Applications Only) or Cool 3 (3-Steps
of Cooling applications). The indoor motor shall be
operating @ 100%, to verify turn DA COOL_FAN SPD
potentiometer full clockwise, voltage should read ~7.5 Vdc
across harness test terminals. The Unit schematic
illustrates location for measuring the indoor motor speed
voltage.
Table 22. Direct drive plenum fan settings (rpm vs.
v
oltage)
Potentiometer Voltage Motor RPM
1 N/A
1.25 N/A
1.5 N/A
1.75 N/A
2 N/A
2.25 325
2.5 402
2.75 465
3 544
3.25 630
3.5 716
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