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7
Dual Fuel Systems
Outdoor split units can be connected to fossil fuel furnaces that
include an A-coil or slab coil. Dual fuel installations utilize the
outdoor split heat pump for heating until the point that auxiliary
heat is called for on the thermostat. At that point, the furnace
will be enabled and the heat pump will be disabled. The outdoor
split heat pump provides air conditioning through the furnace’s
refrigerant coils.
Refer to the furnace manufacturer’s installation manual for
the furnace installation, wiring and coil insertion. A Dual Fuel
thermostat or a field-installed SPST relay is required. See the
Typical Split System Heat Pump Coil Add-on Fossil Fuel Furnace
illustration for typical Dual Fuel application.
Thermostat
Wire From Furnace
Wire To
Thermostat
Up-Flow
Fossil Fuel
Furnace
Condensate
Drain
(must be trapped)
"A" or
Slab Coil
Supply Duct
Insulated
Suction Line
Return
Duct
Lineset To Air Handler
Disconnect
Typical Split System Heat Pump Coil
Add-on Fossil Fuel Furnace
In add-on Outdoor Split applications, the coil should be located
in the supply side of the furnace to avoid condensation damage
to the furnace heat exchanger. A high temperature limit should
be installed upstream of the coil to de-energize the compressor
whenever the furnace is operating. Without this switch, the
Outdoor Split will trip out on high pressure. A dual fuel thermostat
can remove the Y1 and Y2 calls when a W call is energized to
allow gas furnace backup on a Outdoor Split application. Refer to
the Thermostat Wiring section for details.
General Installation Information cont.
AFFINITY DUAL-CAPACITY OUTDOOR SPLIT SERIES INSTALLATION MANUAL