37
SECTION 1 – INSTALLATION
FORM 145.32-IOM5
ISSUE DATE: 04/08/2019
1
AIR TEMPERATURE SENSORS
Each unit is equipped with standard SA temperature
(SAT) and RAT sensors. Sensors ship inside the electri-
cal box, the wire tied to the wiring. In addition to sen-
sors, 8-foot long wiring extensions also ship inside the
In order to insert a temperature sensor, a 5/16-inch hole
must be field drilled in the duct work and the sensor in-
serted through the hole. Small wings keep the sensor se-
cured in the hole.
The RAT sensor can be installed in a pre-punched hole
on the filter frame. There are two holes punched on both
sides of the filter frame, halfway through the height of the
filter frame. The extension wiring can be easily routed out
of the unit through 7/8-inch pre-punched holes that are
located on both sides of the unit.
The location of the sensor has to be chosen according
to local codes and installation practices.
LD27722
FIGURE 18 -
RAT SAT SENSOR
LD27710
FIGURE 19 -
EXTENSION WIRING
VARIABLE FREQUENCY DRIVE (VFD)
This section discusses variable frequency for only 8 and
10 ton units.
Indoor Fan VFD
A standard VFD controller for the evaporator (indoor)
fan applies on 8 to 10 ton models. Mounted in the evap-
orator module section, the VFD allows the operator to
set the duct static pressure or to control discrete indoor
fan speed steps. To meet the desired supply duct static
setpoint or a specific discrete speed step, the VFD con-
trols the evaporator fan motor's frequency (or speed).
For reliable operation, the unit must have a factory in-
stalled hot gas bypass (HGBP) circuit on refrigeration
circuit #1 for units with a duct pressure control option.
Unless requested by the customer as a selectable fea-
ture, the unit setup for discrete speed steps does not
require HGBP for reliable operation.
In 8 ton units, the standard discrete speed step con-
figuration is that the VFD has been setup for the three
discrete speeds, automatically adjusted. The 10 ton
unit features 4 discrete speed steps. In both cases, the
discrete fan speeds are matched and adjusted automati-
cally based on the active cooling stage.
The unit does not carry a failsafe circuit
to bypass the factory installed VFD and
run the evaporator or condenser fan in
the event of a VFD malfunction.
The VFD is factory mounted and wired. The installer must
provide and field install two sensor tubing lines complete
with static pressure probes (except to the configuration
for discrete speed application). The installer must field
wire the fan power wiring between the evaporator VFD
and the unit electrical box (located in the condenser sec-
tion) because the unit ships factory-split. For units with a
static pressure control option, low voltage wiring from the
pressure transducer must be connected to the unit control-
ler (see the unit schematic for more details).
