Nortek FG7SC, Installation Instructions Manual

27

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 the thermostat wires (

R

, 

W

, 

Y

, & 

G

) are securely 

connected to the correct leads on the terminal strip of the 

circuit board.

√

 Verify the jumper on the Nordyne/UTEC board or 

dipswitch on the Emerson board (for fan speed) on the 

control board. See 

Figure 27 (page 25) 

and 

Figure 28 

(page 25)

.

√

 Verify the gas line service pressure does not exceed 10.0 

inches of W.C., 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 red button to reset a switch. DO 

NOT install a jumper wire across a switch to defeat its 

function. If a switch reopens on startup, 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 (

page 28

).

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 6 (page 36)

.

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 6

 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.

6. The manifold pressure must be set to the appropriate 

value for each installation by a qualified installer, service 

agency or the gas supplier.

 WARNING:

Do not attempt to drill the gas orifices. Use only 

factory supplied orifices. Improperly drilled 

orifices may cause fire, explosion, carbon 

monoxide poisoning, personal injury or death.

a.) Obtain the manifold pressure setting required for 

this installation by referring to 

Table 8 (page 37)

 for 

Propane or 

Table 10 (page 38)

 or 

Table 11 (page 

38)

 for Natural Gas.

b.)  Remove the regulator capscrew (

Figure 31

) from the 

INLET side of the regulator.

c.)  Slowly turn the adjustment screw inside the regulator 

to obtain the appropriate manifold pressure.

 NOTE:

 Turning the screw clockwise increases the 

pressure and turning the screw counter-clockwise 

decreases the pressure. To prevent backing the screw 

all the way out from the valve, turn the screw slowly.

d.)  Replace and tighten the regulator capscrew over the 

adjustment screw.

Verifying & Adjusting Temperature Rise

After installation of the furnace, confirm the temperature rise 

of the furnace is within the limits specified on the rating plate. 

Any temperature rise outside the specified limits could result 

in premature failure of the heat exchanger.
1. Place thermometers in the return and supply air stream 

as close to the furnace as possible. The thermometer on 

the supply air side must be shielded from direct radiation 

from the heat exchanger to avoid false readings.

2. Adjust all registers and duct dampers to the desired position 

and run the furnace for 10 to 15 minutes before taking 

any temperature readings. The temperature rise is the 

difference between the supply and return air temperatures.

For typical duct systems, the temperature rise will fall within the 

limits specified on the rating plate with the blower speed at the 

factory recommended setting. If the measured temperature 

rise is outside the specified limits, it may be necessary to 

change the speed of the blower.

NOTE: 

Lowering the blower speed will increase the 

temperature rise and a higher blower speed will decrease 

the temperature rise.

The furnace is equipped with a 5-speed ECM motor. Heating 

and cooling speed selection is made by moving the switch on the 

integrated control inside of the furnace. The furnace is shipped 

Figure 31. Regulator Capscrew

Capscrew