Lennox CBX25UHV-018, Installation Instructions Manual

Page: 17 / 25

Page 17
MERIT
®
CBX25UHV SERIES
BDC3 Blower Control
JP1 15 PIN
PLUG (BOARD
TO MOTOR)
4
3
2
1
TEST
-
+
NORM
ADJUST HEAT COOL DELAY CFM RUN
24V/1A
SERVICE
JP1
24V ACCESSORY
CONTACTS –
RATED FOR 1 AMP
OR LESS
OPERATIONAL
SELECTOR PINS
(AFFECTS BOTH
HEATING AND
COOLING MODES)
DIAGNOSTIC
LEDS
HEATING SPEED
SELECTOR PINS
COOLING SPEED
SELECTOR PINS
FAN DELAY
SELECTOR PINS
4
3
2
1 4
3
2
1
QC1
QC2
Figure 23. BDC3 Variable Speed Control Selections
Merit
®
CBX25UHV 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 BDC3 control.
The jumpers are labeled 1, 2, 3, and 4. This indicates the
selected air volume (CFM). The
ADJUST jumper is
labeled Test, -, +, and Norm. The - and + pin settings 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. The delay jumper controls the timing pattern in
which the fan delay occurs.
Figure 23 illustrates the BDC3 control. Use either table 5
on page 19, or table 6 on page 19, to determine the correct
air volume for heat and cool speed taps.
Diagnostic LEDs located on the BDC3 control to assist in
servicing the unit. Read the jumper settings section before
adjusting blower speed. Refer to figure 23 on page 17 for
identification.
Adjusting the Blower Speed
Diagnostic LEDs
1 - RUN LED indicates there is a demand for the blower
motor to run.
2 - CFM LED indicates the cubic feet per minute at which
the unit is operating. The light flashes once for
approximately every 100 CFM. 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 is
normal and occurs when the control is communicating with
the motor between cycles.
Move the jumper pins to select the blower speed needed to
meet application CFM requirements.
JUMPER SETTINGS
IMPORTANT
Before changing jumper setting, make sure the
motor has completely stopped. Any jumper setting
change will not take place while the motor is
running.
Table 2 lists the recommended factory blower speed tap
selections for Merit
®
CBX25UHV series units. These
settings are for nominal tonnage match-ups with the Merit
®
CBX25UHV. When matched with other sizes, it is
recommended that the CFM be adjusted to provide
approximately 400 CFM per ton.
Table 2. Recommended Blower Speed Taps
Air Handler
Speed Tap Selection
Cooling Heating*
Note 1 - Note 2 - Note 3 - Note 4 -
CBX25UHV­018
COOL
PIN #2 COOL
PIN #2 HEAT
PIN #2 HEAT
PIN #2
CBX25UHV­0
24
COOL
PIN #3 COOL
PIN #3 HEAT
PIN #2+ HEAT
PIN #2+
CBX25UHV­0
30
COOL
PIN #3 COOL
PIN #3 HEAT
PIN #2+ HEAT
PIN #2+
CBX25UHV­0
36
COOL
PIN #3 COOL
PIN #3 HEAT
PIN #2 HEAT
PIN #2
CBX25UHV­0
42
COOL
PIN #3 COOL
PIN #3 HEAT
PIN #2 HEAT
PIN #2
CBX25UHV­0
48
COOL
PIN #3- COOL
PIN #3- HEAT
PIN #2 HEAT
PIN #2
CBX25UHV­0
60
COOL
PIN #3- COOL
PIN #3- HEAT
PIN #2 HEAT
PIN #2
NOTES -
1 - Condensing Unit
2 - Heat Pump
3 - Condensing Unit with electric heat only
4 - Heat Pump with electric heat
* Minimum setting for heat
To change jumper positions, gently pull the jumper off the
pins and insert it onto the desired set of pins. The following
section outlines the different jumper selections available
and conditions associated with each one as illustrated in
figure 23.
After the CFM for each application has been determined,
the jumper settings must be adjusted to reflect those given
in the appropriate tables on the following pages. From the
tables, determine which row of CFM volumes 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.
ADJUST JUMPER
The ADJUST pins allow the motor to run at normal speed,
slightly higher (approximately 10%) than normal speed, or
slightly lower (approximately 10%) than normal speed. The
tables on the following pages list three rows (+, NORMAL,
and -) with their respective CFM volumes. Notice in table 3,
for example, that the normal adjustment setting for heat