Trane WSC036A Installation Operation & Maintenance page 43

2. Measure the amperage at the supply fan contactor and compare it with the full load amp (FLA)
Actual Motor Amps X Motor HP
3. If the required CFM is too low, (external static pressure is high causing motor HP output to be
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Verifying Proper Air Flow (Units with 5-Tap Direct 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 motor is factory wired to operate on speed tap 1 in the cooling and heating mode
for electric/electric units. For Gas/Electric units, the motor is factory wired to operate on speed tap
1 during cooling. For 3 & 4 ton Gas/Electric units operating in heat mode, the minimum setting is
Tap 4. For these units, a separate tap terminal is provided to change speeds automatically between
heating and cooling. The motor can be rewired for different speed settings should the application
require it. Refer to the wiring diagram that shipped in the unit and the unit fan performance tables
in the Service Facts.
The indoor fan motors are specifically designed to operate within the BHP parameters listed in the
fan performance tables of the unit Service Facts.
When verifying direct drive fan performance, the tables must be used somewhat differently than
those of belt driven fans. Fan performance diagnostics can be easily recognized when these tables
are used correctly.
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 Control
Using the Service Test Guide in Table 5, momentarily jump across the Test 1 & Test 2 terminals on
LTB1 one time to start the Minimum Ventilation Test.
With the fan operating properly, determine the total system external static pressure (inches w.c.)
by the following method:
1. Measure the supply and return duct static pressure and sum the resulting absolute values,
2. Use the accessory pressure drop table in the Service Facts, to calculate the total static pressure
Note: Accessory static pressure drop is based on desired CFM and may not be actual static
RT-SVX23D-EN
rating stamped on the motor nameplate.
a. a. Calculate the theoretical BHP
Motor Nameplate Amps
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.
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 and turn sheave clockwise.
To Decrease Fan RPM; Loosen the pulley adjustment set screw and turn sheave
counterclockwise.
If the required CFM is too high, (external static pressure 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 main power disconnect switch to the "Off" position or
proceed to the next component start-up procedure.
drop for all of the accessories installed on the unit; i.e., curb, economizer, etc.
pressure drop.
Start-Up
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