Page 17
SGH/SCH036, 060, 120, 240
Wire runs over 150 feet (mm):
Use a local, isolated 24VAC transformer such as Lennox
cat #18M13 (20VA minimum) to supply power to RH
sensor as shown in figure 19. Use two shielded cables
containing 20AWG minimum, twisted pair conductors
with overall shield. Belden type 8762 or 88760 (plenum)
or equivalent.
FIGURE 19
FIELD WIRING REHEAT UNITS
(Using A Humidity Sensor With
More than 150 Ft. Wire Runs)
ISOLATED 24V
TRANSFORMER
9
8
P298
J298A
1
2
B
3
4
C
5
6
7
D
10
A91
VIN
VO
GND
R
C
AI-1
HUM
TMP
DO-1
C
DI-1
DO-2
NOT
CONNECTED
NOT
CONNECTED
DRAIN
A55 UNIT
CONTROLLER
FIGURE 20
FIELD WIRING REHEAT UNITS
(Using A Dehumidification Switch)
7
10
8
9
R
DI
−
4
C
Use 24 VAC (R) from any terminal
available on J299
−
2,
−
5, or
−
7.
J299
DEHUMIDIFICATION
SWITCH
Blower Operation and Adjustments
Belt Drive With Supply Air Inverter or Direct Drive Units-
The blower rotation will always be correct on units equipped
with an inverter or a direct drive blower. Checking blower
rotation is not a valid method of determining voltage
phasing for incoming power.
Units Equipped With Belt Drive Blowers Controlled by
an Inverter OR Direct Drive Blowers Equipped With
Optional Voltage or Phase Detection -
The Unit
Controller checks the incoming power during start-up. If the
voltage or phase is incorrect, the Unit Controller will display
an alarm and the unit will not start.
A-Blower Operation
Note - On units with staged blowers, use the Unit Controller
to start the blower. Refer to the appropriate start-up section.
Initiate blower demand at thermostat according to instructions
provided with thermostat. Unit will cycle on thermostat demand.
The following steps apply to applications using a typical
electro-mechanical thermostat. MSAV
t
units refer to the
Optional Supply Air VFD section.
1- Blower operation is manually set at the thermostat
subbase fan switch. With fan switch in
ON
position,
blowers will operate continuously.
2- With fan switch in
AUTO
position, the blowers will cycle
with demand. Blowers and entire unit will be off when
system switch is in
OFF
position.
B-Blower Access
The blower assembly is secured to a sliding frame which
allows the blower motor assembly to be pulled out of the
unit. See figure 21, 22, or 23.
Belt Drive Blowers
1- Disconnect wiring to heating limit switches and mixed
air sensor (units with economizer).
2- Remove screws on either side of blower assembly
sliding base. See figure 22 or 23.
3- Pull base toward outside of unit.
Direct Drive Blowers
1- Loosen the reusable wire tie which secures the controls
and high voltage blower wiring to the blower housing.
2- Remove and retain screws in front and on either side of
blower housing. Pull frame toward outside of unit.
3- Slide frame back into original position when finished
servicing. Reattach the blower wiring in the previous
location on the blower motor base using the wire tie.
4- Replace retained screws in front and on either side of
