Page 17
The tables on the following pages list three rows (+, NOR-
MAL, and -) with their respective CFM volumes. Notice in
table 3, 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.
TABLE 3
BLOWER DATA
CBA25UHV-018 BLOWER PERFORMANCE
0 through 0.80 in. w.g. External Static Pressure Range
“ADJUST”
Jumper
Setting
Jumper Speed Positions
“HEAT” Speed First Stage “COOL” Speed Second Stage “COOL” Speed
1 2 3 4 1 2 3 4 1 2 3 4
cfm cfm cfm cfm cfm cfm cfm cfm cfm cfm cfm cfm
+ 500 705 925 1150 365 520 665 810 500 705 925 1150
NORM 465 650 850 1050 350 485 610 740 465 650 850 1050
– 420 600 760 950 320 425 560 680 420 600 760 950
NOTES - The eect of static pressure, lter and electric heater resistance is included in the air volumes listed.
First stage cooling air volume is 70% of COOL speed setting. Continuous blower speed is approximately 50% of COOL speed setting.
Lennox Harmony III™ Zoning System applications - minimum blower speed is 250 cfm.
TABLE 4
BLOWER DATA
CBA25UHV-024 BLOWER PERFORMANCE
0 through 0.80 in. w.g. External Static Pressure Range
“ADJUST”
Jumper
Setting
Jumper Speed Positions
“HEAT” Speed First Stage “COOL” Speed Second Stage “COOL” Speed
1 2 3 4 1 2 3 4 1 2 3 4
cfm cfm cfm cfm cfm cfm cfm cfm cfm cfm cfm cfm
+ 450 670 900 1120 340 450 650 770 450 670 900 1120
NORM 420 620 820 1050 300 400 600 700 420 620 820 1050
– 390 570 750 915 280 390 500 650 390 570 750 915
NOTES - The eect of static pressure, lter and electric heater resistance is included in the air volumes listed.
First stage cooling air volume is 70% of COOL speed setting. Continuous blower speed is approximately 50% of COOL speed setting.
Lennox Harmony III™ Zoning System applications - minimum blower speed is 250 cfm.
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