Trane WSC036A Installation Operation & Maintenance page 42

Start-Up
3. Add the total accessory static pressure drop (step 2) to the duct external static pressure (step
4. Measure the amperage at the supply fan contactor and compare it with the full load amp (FLA)
Example: W_D060 single phase, low speed.
Actual Motor Amp (5.25) = .99%
Motor Nameplate Amps (5.3)
0.99 X Motor HP (0.6) = .59 BHP
The actual external static pressure is approximately 0.45" w.c., airflow equals 2100 CFM.
If the static pressure reading was higher, motor current would have to be lower proportionately to
get an accurate CFM measurement in direct drive applications.
5. If the required CFM is too low, (external static pressure is high causing motor HP output to be
6. If the required CFM is too high, (external static pressure is low causing motor HP output to be
7. To stop the SERVICE TEST, turn the main power disconnect switch to the "Off" position or
Verifying Proper Air Flow (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 adjustable motor sheave.
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
LTB1 one time to start the Minimum Ventilation Test.
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) by;
1. Measuring the actual RPM,
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1). The sum of these two values represents the total system external static pressure.
rating stamped on the motor nameplate.
a. Calculate the theoretical BHP .
Actual Motor Amps X Motor HP
Motor Nameplate Amps
b. Using the fan performance tables in the unit Service Facts, plot the total external static
pressure (step 3) and the BHP (step 4a) to obtain the operating CFM.
c. When plotted, if the two values can not be interpolated correspondingly, the static pressure
will most likely be the least accurate measurement. Because of the direct drive motor
operation, the RPM performance is relatively constant making the operating current a very
reliable diagnostic tool.
below table value),
a. Relieve supply and/or return duct static.
b. Change indoor fan speed to "High" and repeat steps 1 through 4.
above table value), increase supply and/or return duct static.
proceed to the next component start-up procedure.
Table 7, momentarily jump across the Test 1 & Test 2 terminals on
RT-SVX23D-EN