Verifying Proper Air Flow - American Standard YSC036A Installation, Operation And Maintenance Manual

Electro Mechanical 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) by;
1. Measuring the actual RPM,
2. 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 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 is 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 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.
38

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 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.
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
drop for all of the accessories
installed on the unit; i.e., curb,
economizer, etc.
Note: Accessory static pressure
drop is based on desired CFM
and may not be actual static
pressure drop.
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.
Using the Fan Performance Tables in
the Service Facts, look up the
selected speed tap setting and match
the measured ESP to determine the
approximate CFM.
If the required CFM is too low,
(external static pressure is high) do
one or both of the following and
repeat procedure:
a. Relieve supply and/or return
duct static.
b. Change indoor fan speed tap
to a higher value
If the required CFM is too high,
(external static pressure is low), do
one or both of the following and
repeat procedure:
a. Increase supply and/or return
duct static.
b. Change indoor fan speed tap
to a lower value.
Note: Minimum setting for units
with Gas or Electric Heat is
320 CFM per Ton. For 3 & 4
Ton Gas Heat units 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" position or
proceed to the next component
start-up procedure.
RT-SVX21F-EN
Start-Up