Verifying Proper Air Flow; Reliatel Control; Electro Mechanical Control; Start-Up - American Standard YSC036A Installation, Operation And Maintenance Manual

Verifying Proper Air Flow

(Units with Two Speed 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 low speed in the
cooling and heating mode. It can be
rewired for high speed operation
should the application require it.
Refer to the wiring diagram that
shipped in the unit.
The indoor fan motors are
specifically designed to operate
within the BHP parameters listed in
the fan performance tables of the
unit Service Facts. By understanding
that these motors will safely work
within these conditions, before an
oversized motor is required, will
allow the air distribution system to
be set up properly and diagnostics
enhanced should a problem occur.
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 10, momentarily jump across
the Test 1 & Test 2 terminals on LTB1
one time to start the Minimum
Ventilation Test.
Electro Mechanical
Control
Using the Service Test Guide
perform the proper test mode
connections.
RT-SVX21F-EN

Start-Up

With the fan operating properly,
determine the total system external
static pressure (inches w.c.) by;
1. Measuring the supply and return
duct static pressure,
2. Using the accessory pressure
drop table in the Service Facts,
calculate the total static pressure
drop for all of the accessories
installed on the unit; i.e., curb,
economizer, etc.
Note: Static pressure is based on
desired CFM and may not be
actual static pressure.
3. Add the total accessory static
pressure drop (step 2) to the
duct external static pressure
(step 1). The sum of these two
values represents the total
system external static pressure.
4. Measure the amperage at the
supply fan contactor and
compare it with the full load
amp (FLA) 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.
• 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
below table value),
a. Relieve supply and/or return
duct static.
b. Change indoor fan speed to
"High" and repeat steps 1
through 4.
6. If the required CFM is too high,
(external static pressure is low
causing motor HP output to be
above table value), increase
supply and/or return duct static.
7. To stop the SERVICE TEST, turn
the main power disconnect
switch to the "Off" position or
proceed to the next component
start-up procedure.
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
Table 10, momentarily jump across
the Test 1 & Test 2 terminals on LTB1
one time to start the Minimum
Ventilation Test.
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