Nortek MB7EM 3-PHASE Series, Installation Instructions Manual

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9
blower off delay in cooling. See Figure 11 (page 19) , Figure
12 (page 20) , & Figure 13 (page 20) for control board layout
and Table 9, (page 17) for element sequences.
Twinning
These instructions are to be used when connecting two MB7EM
air handlers (2-5 ton models) to a common single stage A/C
condensing unit or heat pump. Twinning is possible for MB7EM
units with fixed speed (FSHE) motors. Twinning is not possible
for units with variable (VSHE) speed motors. All low voltage
wiring instructions, cautions, and warnings accompanying the
air handler remain applicable, except for:
IMPORTANT NOTES:
• If there is any other air moving device in the duct work,
consult the factory for a resolution.
• Variable speed air handlers cannot be twinned. Please
follow the instructions supplied with the kit.
Line & Low Voltage Connections
• The line voltage connections for both air handlers must be
the same phase and on the same leg of power.
• When matched with an S6BQ series AC outdoor unit, both air
handler’s 24V transformers must be removed from the control
circuit by removing and discarding the RED wire located
on the transformer’s secondary. These outdoor units come
standard with 24V power supply sufficient for powering both
air handlers.
• Low voltage wiring should be connected as shown in Figure
10 (page 19) .
• Wire all other low voltage thermostat terminals to both air
handlers as shown in Figure 9 (page 18) .
Heater Kits
Field-installed electric heater kits are available. Instructions
for installing the electric heaters are included with the heaters.
Additional heater kit information can be found in the units
Technical Specifications.
Air handlers set up with 15 kw or more of electric heat will
normally be configured for multiple-circuit power supply. They
may, however, be connected to a single-circuit power supply
with the addition of a single circuit accessory kit. Select the wire
size and over-current protection in accordance with the minimum
circuit ampacity and maximum over-current protection shown in
Table 8, (page 16) . See also the units Technical Specifications.
When electric heat packages with circuit breakers are field-
installed, the circuit breaker may be used as a disconnecting
means in most applications. Reference the NEC and local codes
for disconnect requirements.
If a heater kit is installed:
The MB7 air handler is shipped from the factory without an electric
heater kit installed. If Electric heat is desired, the H8HK heater
kit may be purchased separately and field installed. Determine
the correct size heater kit for your unit by referring to the list
below or the units rating label.
A Size Cabinet (1200 CFM) ........................... 15Kw max
B Size Cabinet ............................................... 20Kw max
C Size Cabinet ............................................... 20Kw max
1. Connect the 2 wire plug of the air handler to the mating 2
wire plug of the heater kit.
2. Connect the line voltage leads to the circuit breaker or terminal
block provided.
3. Connect the heater kit plug with the mating receptacle on the
air handler control board.
If a heater kit is not installed:
1. Remove the 2 wire plug of the air handler by cutting the wires
and discarding the plug.
2. Strip the ends of the 2 air handler wires and connect to the
line-voltage leads with the 2 wire nuts provided.
Humidifier
The unit has an output to power a humidifier when the blower is
running. This output is rated to 1.0 amp at 208/240V. Connection
is made to the HUM terminal on the control board. See Figure
11 (page 19) .
Dehumidification Options
The motor control boards ( Figure 12 & Figure 13 ) have a
DHUM
connection that allows the system to increase the amount
of humidity that is removed from the circulating air. This is
accomplished by reducing the CFM and allowing the cooling coil
to become colder. This will only occur when there is a call for
cooling. There are many ways that this can be electrically wired.
1. If the room thermostat incorporates a humidity sensor and
DHUM
output, connect the
DHUM
on the thermostat to
the
D
terminal on the motor control board. See Figure 6
(page 9) .
2. If using a separate humidistat, connect the DHUM & R terminals
on the humidistat to the D & R terminals on the motor control
board of the air handler. In this option, the DHUM output of
the humidistat must be set so it is only closed when there is
a call for dehumidification.
3. If a humidistat is not available, it is an acceptable option
to connect the R & D terminals on the motor control board
together with a field supplied wire. This option causes the
blower to run at a reduced CFM for 10 minutes after a call
for cooling. NOTE: If outdoor unit is a heat pump, connect
the O terminal to the D terminal.
Electronic Air Cleaner (EAC)
The unit has an output to power an electronic air cleaner when
the blower is running. This output is rated to 1.0 amp at 208/240V.
See Figure 11 (page 19) .
STARTUP & ADJUSTMENTS
Before You Start the Air Handler
Prior to start-up, complete the following inspections:
√
Verify the unit is level and properly located with adequate
clearances for servicing the unit. See Table 1, (page 4) .
√
Check condensate drain line(s) for proper drainage.
√
Verify the surrounding area and top of the unit is free from
obstructions and debris.
√
Check all duct connections. Make sure the duct work is
adequately sealed to prevent air leakage.
√
Check all coil connections for leaks.
√
Verify that the line voltage power leads are securely connected
and the unit is properly grounded. Make sure all doors are
installed before restoring power to the unit
√
Verify the thermostat is wired correctly. Make sure all low
voltage wires are securely connected.
√
Verify the power supply branch circuit overcurrent protection
is sized properly.
√
Verify filter is properly and securely installed.
DHUM
R R
DHUM
HUMIDISTAT
MOTOR
CONTROL BOARD
Figure 6. DHUM Wiring Configuration