Page 9
CBX27UH SERIES
Table 3. Filter Dimensions
CBX27UH
Filter Size − In. (mm)
−018, −024, −030, and −036
20" x 20" (508mm x
508mm)
−042, −048, and −060
20 x 24 (508 x 610)
Sealing the Unit
WARNING
There must be an airtight seal between the bottom of the
air handler and the return air plenum. Use fiberglass
sealing strips, caulking, or equivalent sealing method
between the plenum and the air handler cabinet to
ensure a tight seal. Return air must not be drawn from a
room where this air handler or any gas−fueled appliance
(i.e., water heater), or carbon monoxide−producing
device (i.e., wood fireplace) is installed.
Seal the unit so that warm air is not allowed into the
cabinet. Warm air introduces moisture, which results in
water blow−off problems. This is especially important when
the unit is installed in an unconditioned area.
Make sure the liquid line and suction line entry points are
sealed with either the provided flexible elastomeric thermal
insulation, or field provided material (e.g.
Armaflex
,
Permagum
or equivalent). Any of the previously mention
materials may be used to seal around the main and
auxiliary drains, and around open areas of electrical inlets.
Measuring Static Pressure
1. Measure tap locations as shown in figure 9.
MANOMETER
SUPPLY
RETURN
UNIT SHOWN IN
HORIZONTAL DISCHARGE LEFT POSITION
Figure 9. Static Pressure Test
2. Punch a 1/4" (6mm) diameter hole in supply and return
air plenums. Insert manometer hose flush with inside
edge of hole or insulation. Seal around the hose with
permagum. Connect the zero end of the manometer
to the discharge (supply) side of the system. On
ducted systems, connect the other end of manometer
to the return duct as above. For systems with
non−ducted returns, leave the other end of the
manometer open to the atmosphere.
3. With only the blower motor running and the
evaporator coil dry, observe the manometer
reading. Adjust blower motor speed to deliver the air
desired according to the job requirements.
4. For best air performance external static pressure
drop must not exceed 0.5" W.C. (1.2 kPa). Refer to
blower data tables for cfm and external static.
5. Seal around the hole when the check is complete.
Adjusting Blower Speed
MOTOR SPEED TAPS
NOTE − Motor is programmed for a 45-second delay off on
all speed taps except TAP #1 (continuous fan speed).
Table 4 lists the recommended factory blower speed tap
selections for CBX27UH series units.
Table 4. Recommended Blower Speed Tap Selection
Operation
CBX27UH
Outdoor Unit
Tap
Cooling
ALL SIZES
Condensing unit
3
Heat pump
3
Heating*
Condensing unit with elec-
tric heat only
4
Heat pump with electric heat
4
* Minimum setting for heat
These settings are for nominal tonnage match−ups with the
CBX27UH units. When matched with other sizes, it is
recommended that the CFM be adjusted to approximately
400 CFM per ton.
To change blower motor speed tap remove the speed tap
from Y2 on the terminal strip and insert the desired speed
tap. See table 6 on page 10 for the desired CFM setting.
IMPORTANT
The high-efficiency programmable motor (e.g. X13)
features programmed electronic braking. The integral
control brakes the motor near the end of the supply
blower operation, allowing the motor to maintain a more
controlled ramping shut−down.
Table 5. Motor Speed Taps
Tap Operation
Remarks
1
Continuous or low
speed fan
(for
two−speed heat
pumps or A/C units)
Continuous fan speed is energized (24
volt input to G) when either G or Y1
has a 24 volt signal (24 volt input from
Y1 passes through the room
thermostat’s Fan Automatic contacts
to the G terminal).
2
Low-speed
operation on high
static system
CFM set at 1/2 ton less than nominal
of unit (e.g. 3-ton set at 1000 CFM).
3
Cooling speed
setting
CFM set at 400 cfm per nominal ton at
ARI minimum static allowed, as fol-
lows:
1.5 to 2.0 ton − 0.10
2.5 to 3.5 ton − 0.15
4 to 5 ton − 0.20
4
Heat pump with
electric heat
CFM set at 400 cfm per nominal ton at
.4 static. Energized when electric heat
element has a call for heat.
5
High static
applications
CFM set at 400 cfm per nominal ton at
.8 static.
