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Blower Control Board (A54)
Electric shock hazard. Can cause injury or
death. Before attempting to perform any
service or maintenance, turn the electrical
power to unit OFF at disconnect
switch(es). Unit may have multiple power
supplies.
WARNING
!
15CHAX units are equipped with a variable speed motor
that is capable of maintaining a specified CFM throughout
the external static range. A particular CFM can be obtained
by positioning jumpers (
COOL
,
HEAT
, and
ADJUST
) on
the blower control board. The HEAT and COOL jumpers
are labeled A, B, C and D. Each of the numbers corre-
sponds with an air volume (CFM) setting. The
ADJUST
jumper is labeled Test, −, +, and Norm. The + and − pin set-
tings are used to add or subtract a percentage of the CFM
selected. The Test jumper is used to operate the motor in
the test mode. See figure 8.
Factory settings for the blower speed jumpers are given in
the wiring diagram in figure 7. Figure 8 shows the blower
control board. Use tables 2, 3 and 4 to determine the cor-
rect air volume for operation in heat and cool mode.
The CFM
LED located on the blower control board flashes
one time per 100 cfm to indicate selected blower speed.
For example, if the unit is operating at 1000 CFM,
CFM
LED will flash 10 times. If the CFM is 1150,
CFM
LED will
flash 11 full times plus one fast or half flash.
At times the light may appear to flicker or glow. This takes
place when the control is communicating with the motor be-
tween cycles. This is normal operation.
Read through the jumper settings section before adjusting
the jumper to obtain the appropriate blower speed.
To change jumper positions, gently pull the jumper off the
pins and place it on the desired set of pins. The following
section outlines the different jumper selections available
and conditions associated with each one. Refer to figure 8.
After the CFM for each application has been determined,
the jumper settings must be adjusted to reflect those given
in tables 2, 3 and 4. From the tables, determine which row
most closely matches the desired CFM. Once a specific
row has been chosen (+, NORMAL, or −), CFM volumes
from other rows cannot be used. Below are descriptions of
the jumper selections.
The variable speed motor slowly ramps up to and down
from the selected air flow during both cooling and heating
demand. This minimizes noise and eliminates the initial
blast of air when the blower is initially energized.
ADJUST
The
ADJUST
pins allow the motor to run at normal speed,
approximately 15 percent higher, or approximately 15 per-
cent lower than normal speed. Tables 2, 3 and 4 give three
rows (+, NORMAL, and −) with their respective CFM vol-
umes. Notice that the normal adjustment setting for cool
speed position D in table 2 is 900 CFM. The + adjustment
setting for that position is 1035 CFM and for the − adjust-
ment setting is 765 CFM. After the adjustment setting has
been determined, choose the remaining speed settings
from those offered in the table in that row.
The TEST pin is available to bypass the blower control and
run the motor at approximately 70 percent to make sure
that the motor is operational. This is used mainly in trouble-
shooting. The G terminal must be energized for the motor
to run.
BLOWER CONTROL BOARD (A54)
16−PIN PLUG
(BOARD TO MOTOR)
ADJUST
SELECTOR PINS
(Setting affects both
heating and cooling
modes)
DIAGNOSTIC
LED
HEATING SPEED
SELECTOR PINS
COOLING SPEED
SELECTOR PINS
Figure 8
