Geostar ASTON Series Installation Manual page 7

General Installation Information cont.
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.
Typical Split System Heat Pump Coil
Add-on Fossil Fuel Furnace
ASTON & ASTON ADVANCED DUAL-CAPACITY OUTDOOR SPLIT SERIES INSTALLATION MANUAL
Disconnect
Insulated
Suction Line
Lineset T o Air Handler
Thermostat
Wire From 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.
Supply Duct
"A" or
Slab Coil
Wire T o
Thermostat
Return
Duct
7
Condensate
Drain
(must be trapped)
Up-Flow
Fossil Fuel
Furnace