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Shorting the jumpers for a period of 5 to 20 seconds by-
passes the remaining continuous run period and places the
unit in a Forced Defrost mode. If the controlling DFT is
closed when this mode is initiated, the unit will complete a
normal defrost period that will terminate when the con-
trolling DFT opens or the 10 minute defrost cycle limit is
reached. If the controlling DFT is open when this mode is
initiated, the Defrost cycle will run for 30 seconds. Both
modes end at the end of the Defrost cycle.
ELECTRIC HEATERS
The RHW units may be equipped with field-installed acces-
sory electric heaters. The heaters are modular in design,
with heater frames holding open coil resistance wires strung
through ceramic insulators, line-break limit switches and a
control contactor.
Heater modules are installed in the compartment below the
indoor (supply) fan outlet. Access is through the indoor ac-
cess panel. See Fig. 32-34.
Not all available heater modules may be used in every unit.
Use only those heater modules that are UL listed for use in
a specific size unit. Refer to the label on the unit cabinet for
the list of approved heaters.
Refer to the Small Roof Top Units Accessory Electric Heat-
er and Single Point Box installation instructions for further
details.
Fig. 32 — Typical Access Panel Location
OPTIONAL
SINGLE
FACTORY-
MAIN
INSTALLED
CONTROL
POINT
DISCONNECT
BOX
BOX
CONTROL WIRE
TERMINAL BLOCK
Fig. 33 — Typical Component Location
20
INDOOR
ACCESS
PANEL
CONTROL BOX
ACCESS PANEL
CENTER
VANE AXIAL
POST
INDOOR FAN
SYSTEM
MANUAL
RESET
LIMIT
SWITCH
HEATER
HEATER
MOUNTING
COVER
BRACKET
Specifications subject to change without notice.
Fig. 34 — Typical Heater Module Installation
SINGLE
POINT
BOXES AND
FUSES
When the unit MOCP device value exceeds 60-A, unit-
mounted supplementary fuses are required for each heater
circuit. These fuses are included in accessory Single Point
Boxes, with power distribution and fuse blocks. The single
point box will be installed directly under the unit control box,
just to the left of the partition separating the indoor section
(with electric heaters) from the outdoor section. The Single
Point Box has a hinged access cover. See Fig. 35. The Sin-
gle Point Box also includes a set of power taps and pigtails
to complete the wiring between the Single Point Box and
the unit's main control box terminals. Refer to the Small
Roof Top Units Accessory Electric Heater and Single Point
Box installation instructions for details on tap connections.
All fuses on RHW units are 60-A. (Note that all heaters are
qualified for use with a 60-A fuse, regardless of actual heat-
er ampacity, so only 60-A fuses are necessary.)
SINGLE POINT BOXES WITHOUT FUSES
Unit heater applications not requiring supplemental fuses
require a special Single Point Box without any fuses. The
accessory Single Point Boxes contain a set of power taps
and pigtails to complete the wiring between the Single Point
Box and the unit's main control box terminals. Refer to ac-
cessory heater and Single Point Box installation instructions
for details on tap connections.
CONTROL WIRING
FOAM
POWER
WIRING
Fig. 35 — Typical Single Point Installation
HEATER
MODULE
SUPPLEMENTARY
HEATER
HEATER
RELAY
MOUNTING SCREWS
20
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