5-565.1
24
(40) motor starter – (oPt)
The motor starter is factory installed in the electrical section.
A motor starter is required for all three phase motors and single
phase motors 2 Hp and greater. The motor starter current set
point dial is factory set to the motor full load amp draw listed on
the motor nameplate.
(40) variable frequency drive – (oPt)
The VFD controller adjusts the motor rpm to vary the unit air
flow. The minimum air flow may be varied between 30 and 100%
of the full speed air flow depending on the controls selection of
the unit. The control changeover options are two speed, floating
building pressure sensing, and building management control.
The overload module of the motor starter is designed to trip to
protect the motor from exceeding the nameplate amps. If the
motor exceeds the amp draw on the current set point dial, the trip
condition is indicated by a red color in the trip indicator window.
The motor starter can be placed in the automatic or manual
reset positions. Automatic reset is accomplished by depressing
the “RESET” button and turning the button 1/4 turn. When in the
automatic reset position, if the overload module trips, the module
will reset itself once the overload relay has cooled. In the manual
reset position, if the overload module trips, the “RESET” button
must be depressed before the blower can operate.
The contractor module includes one (1) normally open auxiliary
contact. The contact rating is 10 amps.
If the factory installed motor starter option was not ordered with a
unit that has a three phase motor or single phase motor 2 Hp or
greater, a motor starter must be field supplied and installed.
(42) Proportional temperature controller – (oPt)
A proportional temperature controller is provided with Air Control
options GF, GG, GH, GK, GM, or GN (Digits 20 & 21) and factory
installed in the electrical section. The controller compares the
mixed air temperature set point and the mixed air temperature
from the Proportional Temperature Controller Sensor. The
controller sends a 2-10 Vdc signal to the modulating damper
actuator in order to maintain the set point. The controller includes
a set point dial that must be field set to the desired mixed air
temperature (typically 55°F).
(43) Warm-up stat – (oPt)
A warm-up stat is provided with Air Control options GK, GM, or
GN (Digits 20 & 21) and factory installed in the electrical section
with the sensor in the return air stream. The warm-up thermostat
monitors the return air temperature to the unit and prevents
the fresh air dampers from opening until the temperature of the
return air has reached the desired set point (typically 65°F or 5°F
below the room temperature).
figure 24.2 - Proportional temperature controller
(44) Blower supply Power terminal strip – (std)
The blower supply power terminal strip is located in the electrical
section. The terminal strip is labeled to match the electrical wiring
diagram provided with the unit. Supply power labeling ranges
from terminal numbers 80 to 99. All field wiring connections
should be made to the bottom side of the terminals to prevent
miswiring by modifying the factory wiring which is made to the
top of the terminal strip.
(45) service switches – (oPt)
The service switches are factory installed in the electrical
section. The service switches allow for service personnel to
independently test operation of the damper, blower, and furnace
without using jumper wires. The switches override the remote
monitoring panel and/or thermostats to energize each compo-
nent directly. All switches need to be reset to the “OFF” position
after testing otherwise the components will remain energized.
(46) electronic modulation amplifier – (oPt)
An electronic modulation amplifier is provided factory installed
in the duct furnace electrical junction box when the unit is
equip ped with Electronic Modulating Gas Controls (Digit 12 =
4 or 5). The amplifier processes the thermostat temperature
and set point signals to modulate the firing rate between 40%
to 100% full fire. For additional information, refer to Control
Operating Sequence.
oPtions
DIAL
SET POINT
4 8 12 16 25
2 4 6 8 10
VOLTS
MILLIAMPS
CONTROLS
JOHNSON
A350 P
ON
RESET
WINDOW
INDICATOR
TRIP
DIAL
SET POINT
CURRENT
H
A R
E
S
E
T
NC
NO
96
95
97
98
T3
6
T2
4
T1
2
A2
14
NO
6
T3
4
T2
T1
2
NO
13
L3
5
L2
3
A2
L1
1
A1
CONTACTOR
MODULE
OVERLOAD
MODULE
figure 24.1 - motor starter
figure 24.3 - service switches
