Unitary products group GM8S Installation Manual Download Page 10

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035-20464-002 Rev. A (1004)

Unitary Products Group

SUPPLY VOLTAGE CONNECTIONS

Provide a power supply separate from all other circuits. Install
overcurrent protection and disconnect switch per local/national
electrical codes. The switch should be close to the unit for conve-
nience in servicing. With the disconnect or fused switch in the OFF
position, check all wiring against the unit wiring label. Refer to the
wiring diagram in this instruction.

Remove the screws retaining the wiring box cover. Route the
power wiring through the opening in the unit into the junction box
with a conduit connector or other proper connection. In the junc-
tion box there will be three wires, a Black Wire, a White Wire and a
Green Wire. Connect the power supply as shown on the unit-wir-
ing label on the inside of the blower compartment door or the wir-
ing schematic in this section. The black furnace lead must be
connected to the L1 (hot) wire from the power supply. The white
furnace lead must be connected to neutral. Connect the green fur-
nace lead (equipment ground) to the power supply ground. An
alternate wiring method is to use a field provided 2” (5.1 cm) x 4”
(10.2 cm) box and cover on the outside of the furnace. Route the
furnace leads into the box using a protective bushing where the
wires pass through the furnace panel. After making the wiring con-
nections replace the wiring box cover and screws. Refer to Figure
10.

The furnace's control system requires correct polarity of the power
supply and a proper ground connection. Refer to Figure 11.

IMPORTANT:

The power connection leads and wiring box may be relo-

cated to the left side of the furnace. Remove the screws and cut wire tie
holding excess wiring. Reposition on the left side of the furnace and fas-
ten using holes provided.

LOW VOLTAGE CONTROL WIRING CONNECTIONS

Install the field-supplied thermostat by following the instructions that
come with the thermostat. With the thermostat set in the OFF position
and the main electrical source disconnected, connect the thermostat
wiring from the wiring connections on the thermostat to the terminal
board on the ignition module, as shown in Figure 7. Electronic thermo-
stats may require the common wire to be connected as shown with the
dashed line in Figure 7 or 8. Apply strain relief to thermostat wires pass-
ing through cabinet. If air conditioning equipment is installed, use ther-
mostat wiring to connect the Y and C terminals on the furnace control
board to the proper wires on the condensing unit (unit outside). Refer to
Figure 7.

IMPORTANT:

Set the heat anticipator in the room thermostat to 0.10

amps. Setting it lower will cause short cycles. Setting it higher will cause
the room temperature to exceed the set points.

IMPORTANT:

Some electronic thermostats do not have adjustable heat

anticipators. They may have other type cycle rate adjustments. Follow
the thermostat manufacturer's instructions.

The 24-volt, 40 VA transformer is sized for the furnace components
only, and should not be connected to power auxiliary devices such as
humidifiers, air cleaners, etc. The transformer may provide power for an
air conditioning unit contactor.

ACCESSORY CONNECTIONS

The furnace control will allow power-switching control of various acces-
sories. Refer to Figure 13, for connection details.

ELECTRONIC AIR CLEANER CONNECTION

Two 1/4” (6.4 mm) spade terminals (EAC and EAC N) for electronic air
cleaner connections are located on the control board. The terminals
provide 115 VAC (1.0 amp maximum) during circulating blower opera-
tion.

HUMIDIFIER CONNECTION

Two 1/4” (0.64 cm) spade terminals (HUM and HUM N) for humidifier
connections are located on the control board. The terminals provide 115
VAC (1.0 amp maximum) during heating system operation.

FIGURE 9:

Electrical Wiring

Y W RGC

CLASS 2 SYSTEM
CONTROL WIRING
TO THERMOSTAT

TRANSFORMER

IGNITION MODULE

BURNER COMPARTMENT

BLOWER COMPARTMENT

DOOR SWITCH

JUNCTION
BOX

BLK/BLK
WHT/WHT
GRN/GRN

L1
HOT