121
Table 94 — VFD Terminal Designations
POWER EXHAUST — The units can be equipped with an
optional power exhaust system. The power exhaust fans are
two belt-drive forward-curved fans. On non-modulating sys-
tems, the fans are staged by the ComfortLink™ controls based
on the economizer damper position. For modulating (CV or
VAV) applications, the fans are turned on by the ComfortLink
control based on building pressure sensed by the building pres-
sure transducer. The fan output is modulated via discharge
dampers with LEN communicating actuators to maintain the
building pressure set point.
HIGH CAPACITY POWER EXHAUST (Sizes 075-105
Only) — The power exhaust fans are two belt-driven forward-
curved fans. Operation of the power exhaust is a combination
modulating/staged control. The lead fan is controlled by a VFD
and provides 0 to 50% of total exhaust capability. The second
fan is staged On/Off (for a step of 50% of total exhaust capabil-
ity) according to the VFD output level on fan no. 1.
RETURN/EXHAUST FAN (Sizes 075-105 Only) — The
return/exhaust fan power exhaust assembly consists of one
belt-drive plenum fan. The plenum fan pressurizes the plenum
fan section so that the air can either be discharged horizontally
out the back of the unit or discharged through the return air
section of the economizer.
ECONOMIZER MOTOR(S) — The economizer outside air
and return air dampers are gear-driven dampers without linkag-
es. An LEN communicating economizer motor(s) controls
their position. The motor position is controlled by the MBB
through the LEN communication bus. This allows for accurate
control of the motors as well as feedback information and diag-
nostics information. The control has a self-calibration routine
that allows the motor position to be configured at initial unit
start-up. The motor(s) is located on the economizer and can be
reached through the filter access door.
THERMISTORS AND PRESSURE TRANSDUCERS —
The unit is equipped with several thermistors for measurement
of temperatures. The thermistors are summarized in Table 95.
The units have two pressure transducers that are connected
to the low side of the system. These two pressure transducers
measure the low side pressure and are used for low pressure
protection and coil freeze protection.
The units also have two pressure transducers that are con-
nected to the high side of the system. These two pressure trans-
ducers measure the discharge pressure and are used to cycle the
condenser fans to maintain head pressure.
By using the high and low side pressure transducers, the
ComfortLink controls display the high and low side pressures
and saturation temperatures and a normal gage set is not
required.
SMOKE DETECTOR — The units can be equipped with an
accessory smoke detector located in the return air. The detector
is wired to the ComfortLink controls and, if activated, will stop
the unit by means of a special fire mode. The smoke detector
can also be wired to an external alarm system through TB201
terminals 5 and 6. The sensor is located in the return air section.
FILTER STATUS SWITCH — The units can be equipped
with an optional filter status switch. The switch measures the
pressure drop across the filters and closes when an adjustable
pressure set point is exceeded. The sensor is located in the re-
turn air section behind the filter access door.
TERMINAL FUNCTION
U1
V1
W1 Three-Phase Main Circuit Input Power Supply
U2
V2 Three-Phase AC Output to Motor, 0 V to
W2 Maximum Input Voltage Level
X1-11 (GND)
X1-12 (COMMON) Factory-supplied jumper
X1-10 (24 VDC)
X1-13 (DI-1) Run (factory-supplied jumper)
X1-10 (24 VDC) Start Enable 1 (factory-supplied jumper). When
X1-16 (DI-4) opened the drive goes to emergency stop.
X1-2 (AI-1)
X1-3 (AGND) Factory wired for 4 to 20 mA remote input
Fig. 31 — VFD Wiring