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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.
Tables 1 and 2 list the recommended factory blower speed
tap selections for Merit
®
CBA25UHV series units. These
settings are for nominal tonnage match-ups with the Mer-
it
®
CBA25UHV. When matched with other sizes, it is rec-
ommended that the CFM be adjusted to provide approxi-
mately 400 CFM per ton.
TABLE 1. Recommended Blower Speed Taps
Air Handler
Speed Tap Selection
Cooling Heating*
Note 1 - Note 2 - Note 3 - Note 4 -
CBA25UHV018
COOL
PIN #2
COOL
PIN #2
HEAT
PIN #2
HEAT
PIN #2
CBA25UHV024
COOL
PIN #3
COOL
PIN #3
HEAT
PIN #3
HEAT
PIN #3
CBA25UHV030
COOL
PIN #3
COOL
PIN #3
HEAT
PIN #3
HEAT
PIN #3
CBA25UHV036
COOL
PIN #3
COOL
PIN #3
HEAT
PIN #3
HEAT
PIN #3
CBA25UHV042
COOL
PIN #3
COOL
PIN #3
HEAT
PIN #3
HEAT
PIN #3
CBA25UHV048
COOL
PIN #3
COOL
PIN #3
HEAT
PIN #3
HEAT
PIN #3
CBA25UHV060
COOL
PIN #3
COOL
PIN #3
HEAT
PIN #3
HEAT
PIN #3
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 o the
pins and insert it onto the desired set of pins. The following
section outlines the dierent jumper selections available
and conditions associated with each one as illustrated in
table 2.
After the CFM for each application has been determined,
the jumper settings must be adjusted to reect 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 specic row has been
chosen (+, NORMAL, or -), CFM volumes from other rows
cannot be used. Below are descriptions of the jumper se-
lections.
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 (+, NOR-
MAL, and -) with their respective CFM volumes. Notice in
table 2, for example, that the normal adjustment setting for
heat speed position #4 is 1000 CFM. The + adjustment
setting for that position is 1080 CFM and for the - adjust-
ment setting is 910 CFM. After the adjustment setting has
been determined, choose the remaining speed jumper
settings from those oered in the table in that row.
The TEST pin is available to bypass the BDC3 control and
run the motor at approximately 70% to test that the motor
is operational. This is benecial primarily in troubleshoot-
ing. G must be energized for motor to run.
COOL JUMPER
The COOL jumper is used to determine the CFM during ei-
ther cooling or heat pump operation without a call for elec-
tric heat. These jumper selections are activated for cooling
when Y2 and DS terminals in the Merit® CBA25UHV are
energized. The are activated for heating when Y2 is en-
ergized.
Applications without the Lennox ComfortSense® 7500
thermostat will provide 70% of the COOL CFM during rst-
stage cooling for two-stage outdoor units. 100% of COOL
speed is provided for systems with a single-stage outdoor
unit.
Applications with the Lennox ComfortSense® 7500 ther-
mostat, but no demand for de-humidication will operate
as follows: during a rst-stage cooling call (two-stage
outdoor unit), the air volume is 70% of the COOL jumper
selection. This arrangement provides for additional dehu-
midication during standard rst-stage cooling. See the
tables that follow for various scenarios concerning use
of the ComfortSense® 7500 thermostat and the Merit®
CBA25UHV series unit.
For applications with Harmony III® zone control, the air
handler CFM volume is determined by the Harmony III
control center. The minimum blower speed is predeter-
mined at 250 CFM for -018, -024, -030 and -036 units and
450 CFM for -042, -048 and -060 units. This speed is not
adjustable. See footnotes in the blower performance ta-
bles.
With the thermostat set for Continuous Fan and without
a call for heating or cooling, the Merit® CBA25UHV pro-
vides 50% of the COOL CFM selected.
NOTE - For two-stage heat pumps, air handler will operate
at 70% of the COOL selection until supplemental electric
heat is demanded. At that time, the air handler will operate
at the selected HEAT speed. This arrangement provides
warmer supply air during second-stage heating.
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