MG2S Installation Manual

23
Figure 19. Wiring Configuration 1
R DHUM
C
Y
G
W
1
ROOM THERMOSTAT
(SINGLE STAGE)
DHUM
A/C CONDENSING UNIT
(SINGLE STAGE)
C
R
C
Y/Y2
Y
W2
G
W1
Y1
HIGH EFFICIENCY
BLOWER MOTOR
CONTROL BOARD
TWO STAGE FURNACE BOARD
Figure 20. Wiring Configuration 2
DHUM
A/C CONDENSING UNIT
(SINGLE STAGE)
HIGH EFFICIENCY
BLOWER MOTOR
CONTROL BOARD
C
Y
R DHUMC
Y
G
ROOM THERMOSTAT
(TWO - STAGE)
W
1
W
2
TWO STAGE FURNACE BOARD
R
C
Y/Y2
W2
G
W1
Y1
Autostaging for Two-Stage Thermostats
The Autostage setting on the furnace control board (Figure
27 (page 33)) is disabled when shipped from the factory.
This feature will be not used when paired with a two-stage
thermostat. The autostage jumper setting (P7) must be
kept on OFF to allow the thermostat to adjust stages.
CAUTION:
The terminal marked “Y1_IN” on the variable
speed motor control board is not an output to
drive the outdoor unit. DO NOT connect Y1_IN
on the motor control board to the outdoor unit.
Fixed Speed Blower Applications
The fixed speed motor control board (Figure 26 (page
33)) contains a set of dip switches for setting the blower
speed. Use pins 1 to 4 to set the blower speed for heating
and pins 5 to 8 to set the speed for cooling. To determine
the appropriate switch settings for your installation, see
Table 6 (page 31) and Table 7 (page 32).
For thermostats with a dehumidifier output, use a field
supplied wire to connect the thermostat’s dehumidifier
output to the terminal marked DEHUM. The thermostat
should be set so that the DEHUM output should be high
(positive) when dehumidification is needed.
START-UP & ADJUSTMENTS
Pre-Start Check List
√ Verify the polarity of the connections are correct, the
line voltage power leads are securely connected and
the furnace is properly grounded.
√ Verify that all needed thermostat wires are securely
connected to the correct leads on the terminal strip of
the circuit board. See Figure 19 & Figure 20.
√ Verify the gas line service pressure does not exceed
10.0 inches of water column, and is not less than 4.5
inches W.C. for natural gas. For LP gas the line service
pressure must not exceed 14 in. W.C., and must not
be less than 11.0 in. W.C.
√ Verify the roll-out and manual reset switch is closed.
If necessary, press the button to reset the switch. DO
NOT install a jumper wire across a switch to defeat
its function. If a switch reopens on start-up, DO NOT
reset the switch without identifying and correcting
the fault condition.
√ Verify the blower door is in place, closing the door
switch in the line voltage circuit.
√ Verify the gas line has been purged and all connections
are leak free.
Start-up Procedures
Do not perform these steps until all of the checks in the
previous steps have been completed:
1. Set the thermostat to the lowest setting.
2. Turn off all electrical power to the furnace.
3. Follow the Operating Instructions on the label attached
to the furnace.
4. Set the thermostat above room temperature and verify
the Operating Sequence. See page 25.
5. After 5 minutes of operation, set the thermostat below
room temperature and verify steps 9 - 10 of the Operating
Sequence.
Verifying & Adjusting Input Rate
The input rate must be verified for each installation to
prevent over-firing of the furnace. NOTE: The input rate
must not exceed the rate shown on the furnace rating plate.
At altitudes above 2,000 feet, it must not exceed that on
the rating plate less 4% for each 1,000 feet. To determine
the exact input rate, perform the following procedures:
1. Shut off all other gas fired appliances.
2. Start the furnace and run it for at least 3 minutes.
3. Measure the time (in seconds) required for the gas
meter to complete one revolution.
4. Convert the time per revolution to cubic feet of gas per
hour using Table 9, (page 35).
5. Multiply the gas flow rate in cubic ft per hr by the heating
value of the gas in Btu per cubic ft to obtain the input
rate in Btuh. See example.
Example:
• Time for 1 revolution of a gas meter with a 1 cubic
ft dial = 40 seconds.
• From Table 9 read 90 cubic ft gas per hr.
• Local heating value of the gas (obtained from gas
supplier) = 1,040 Btu per cubic ft.
• Input rate = 1,040 x 90 = 93,600 Btuh.