Geostar ASTON SERIES Installation Manual page 7

General Installation Information cont.
Dual Fuel Systems
Indoor split units can be connected to fossil fuel furnaces that
include an A-coil or slab coil. Dual fuel installations utilize the
geothermal 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 geothermal
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, a field-installed SPST relay or dual capacity
auxiliary heat relay is required. See Figure 2 for typical Dual
Fuel application.
Figure 2: Typical Split System Heat Pump Coil Add-On Fossil Fuel Furnace
Maximum Recommended Distance
Disconnect
Insulated Suction Line
Lineset T o Air Handler
is 60' Between Units
"A" or
Slab Coil
Wire T o
Thermostat
Thermostat
Wire From
Air Handler
DHW Out
DHW In
P/T Plugs
Water Out
Water In
Vibration Absorbing Pad or Air Pad
ASTON INDOOR SPLIT SERIES INSTALLATION MANUAL
In add-on indoor 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
indoor 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 indoor split application. Refer to
thermostat wiring diagram for details.
Supply Duct
Return
Duct
7
Air Temperature Limit Switch -
to prevent compressor operation
when entering air is greater than
90°F.
Condensate
Drain
(must be trapped)
Up-Flow
Fossil Fuel
Furnace