Specifications

7
VI. ELECTRICAL SERVICE
Note – Always refer to the inside of the electrical box
cover for the correct wiring diagram, and always refer to
the nameplate on the exterior of the cabinet for the correct
electrical specifications.
WARNING – ELECTRICAL SHOCK CAN CAUSE
PERSONAL INJURY OR DEATH. Disconnect all power
supplies before installing or servicing electrical devices.
Only trained and qualified personnel should install, repair or
service this equipment.
WARNING – THE UNIT MUST BE PROPERLY
GROUNDED!
The main electrical service must be protected by a fuse or
circuit breaker and be capable of providing the amperes
required by the unit at nameplate voltage. All wiring must
comply with the national electrical code and/or any local
codes that may apply. Access to the line voltage connection
is through the knockouts provided on the side next to the
front. Route EMT or flexible conduit with appropriate size
and type of wire.
CAUTION – Route field wiring to avoid contact with
electrically live bare metal parts inside the electrical box.
CAUTION – Disconnect power from the unit before
removing or replacing any connectors, or servicing the
blower motor.
CAUTION – When servicing an ECM blower motor,
disconnect power and wait at least 5 minutes before opening
the motor to avoid electric shock from the motor’s internal
capacitors.
CAUTION – Units with internal installed Supplemental
Electric Heat require a separate power supply for the
Supplemental Electric Heat.
VII. 24 VOLT CONTROL CIRCUIT
Note – Always refer to the inside of the electrical box
cover for the correct wiring diagram.
Important – All 24V control wiring should be 18 gage
minimum.
There are two basic sections of the low voltage circuit;
transformer and internal controls.
A. Transformer
An internal transformer provides 24Vac for all control
features of the AHU, the room thermostat, the Split System
Controller in the CU, and the Y
2
power to the CU. The
transformer is larger than the industry standard, but it is in a
warm electrical box and can be overloaded quickly.
Transformer Usage (VA)
Component
VA
Room Thermostat
1
Blower Motor Control
2
Split System Controller
2
Y
2
Output to CU
4
Electric Heat Relay (2)
12
Total
21
Transformer VA size
55
Important – If the system’s external controls require
more than shown in table 5, an external transformer and
isolation relays should be used.
Important – Miswiring of 24Vac control voltage on
system controls can result in transformer burnout.
Important – Units with a dual voltage rating (example,
208/230) are factory-wired for the higher voltage (example,
230). If connected to a power supply having the lower
voltage, change the wiring to the transformer primary to the
correct lead; otherwise premature failure, or inability to
operate the control components may occur.
B. Internal Controls
The internal controls perform the following functions:
1) ECM Blower Motor Control
2) Supplemental Electric Heat for 2
nd
Stage Heat.
1. ECM Blower Operation (-xxV)
When 24Vac is applied to the G terminal on the AHU
wiring block, the ECM blower motor will run at Low speed.
When 24Vac is applied to both the G and the Y terminals on
the fan coil wiring block for 1
st
stage operation, the ECM
blower motor will run at Medium speed. When 24Vac is
applied to both the G and the Y
2
terminals for 2
nd
stage
operation, the ECM blower will run at Medium-High speed.
The ECM blower will run at High speed when 24Vac is
applied to either the W or the E terminal.
CFM outputs for the ECM blower are factory set and should
not be changed in the field other than the Adjust setting,
which allows the blower to operate at +/-10% of the factory
setting. For example, if the Adjust tap is set to the “-“, all
the speeds will operate at 90% of the factory setting. If the
Adjust tap is set to the “+”, all the speeds will operate at
110% of the factory setting. The Adjust tap is the only tap
on the Blower Speed Controller that should ever be moved
from the factory setting.
Important – Power to the unit must be reset before the
new settings are enabled. The blower motor also provides
internal circuitry that will try to maintain the setpoint CFM
when changes occur in the external static pressure, such as
the filter getting dirty over time. The motor does this by
increasing its torque output to compensate.
Important – The ECM motor is Factory programmed
with delay profiles for start and stop to ensure the blower
motor slowly ramps up to the proper CFM output and backs