MG2S Installation Manual

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white wire and the incoming HOT line is connected
to the black wire. The furnace will not operate unless
the polarity and ground are properly connected as
shown in Figure 25 (page 33).
Grounding
WARNING:
To minimize personal injury, the furnace cabinet
must have an uninterrupted or unbroken electrical
ground. The controls used in this furnace require
an earth ground to operate properly. Acceptable
methods include electrical wire or conduit
approved for ground service. Do not use gas
piping as an electrical ground!
Thermostat / Low Voltage Connections
• The furnace is designed to be controlled by a 24 VAC
thermostat. The thermostat’s wiring must comply with
the current provisions of the NEC (NFPA 70) and with
applicable local codes having jurisdiction.
• The thermostat must be installed according to the
instructions supplied by the thermostat manufacturer.
Low voltage connections (24 VAC) from the thermostat
are wired to the terminal strip on the integrated control
in the furnace. For heating applications, Figure 19 &
Figure 20 (page 23) show how to properly connect
single stage and two-stage thermostats. Recommended
minimum wire gauge for thermostat wiring is shown in
Table 8, (page 33).
• The thermostat should be mounted about 5 feet
above the floor on an inside wall. DO NOT install the
thermostat on an outside wall or any other location
where its operation may be adversely affected by radiant
heat from fireplaces, sunlight, or lighting fixtures, and
convective heat from warm air registers or electrical
appliances. Refer to the thermostat manufacturer’s
instruction sheet for detailed mounting information.
Single Stage AC & Single Stage Thermostat
This option does not use the full two-stage control
capability of the furnace, but the possibility of timed
autostaging is available. See also Autostaging for Single
Stage Thermostats.
• Connect the thermostat’s W output to the furnace
control boards W1 terminal. This allows the furnace
to always run in low output mode. See (Figure 19)
• Always connect the thermostat C & R to the furnace
control board C & R.
• For cooling, connect the thermostats Y signal to the
furnace control board Y / Y2 terminal.
• Field supplied wires should also connect Y / Y2 & C
to the outdoor unit’s Y & C terminals.
Single Stage AC & Two Stage Thermostat
This option uses the full two stage heating capability of the
furnace with a single stage outdoor unit. See Figure 20.
• Connect the thermostat’s W1 & W2 outputs to the
furnace control board’s W1 & W2 terminals.
• Always connect the thermostat C & R to the furnace
control board C & R
• For cooling, connect the thermostats Y signal to the
furnace control board Y / Y2 terminal.
• Field supplied wires should also connect Y / Y2 & C
to the outdoor unit’s Y & C terminals.
Autostaging for Single Stage Thermostats
The Autostaging feature makes it possible to use a single
stage thermostat and still receive some of the benefits
of 2-stage furnace operation. If Autostage is enabled,
the furnace will drop to LOW fire after initially starting
in HIGH fire. After a period of 10 minutes, the furnace
will then stage up to HIGH fire, until the heating load is
met. See Figure 19 (page 23) and the Low Voltage
Connection section.
The autostaging option is selected using the autostage
jumper located near the thermostat terminal block. See
Figure 27 (page 33). When the autostage jumper is
moved from OFF to ON, the following occurs during a
call for heat:
Setting the Autostage jumper in the ON position signals
the control to utilize a 10 minute delay between LOW fire
and HIGH fire when a call for heat is supplied via 24V
signal to W1.
NOTE: If the autostage jumper is in the ON position and
a W1 demand is present when power is applied to the
furnace, the first heat cycle will run in second stage heat
with no autostaging. After the first cycle, the furnace will
resume normal autostaging operation.