•
CHECKING FURNACE INPUT
Checking the furnace input is
important to prevent overtiring the
furnace. NEVER SET THE INPUT
ABOVE THAT SHOWN ON THE
RATING PLATE. Use the following
table or formula to determine the
input rate.
Prior to checking input. make certain
that all other gas appliances are shut
off with the exception of pilot
burners.
Start the furnace and note the time
needed to burn one cubic foot of gas.
Time the meter with only the furnace
operating.
Do not make any attempt to derate
the furnace below 8000' by changing
gas orifices or the gas pressure.
Allow the natural derate of the gas to
occur. The natural derate is
approximately 1 .8% per 1000 feet.
No orifice sizing or other derate
procedures are necessary below
8000' unless the natural gas BTU
content exceeds 1075 BTU/ft
3
at sea
level or the LP gas BTU content
exceeds 2500 BTU/ft
3
at sea level. If
the heating values exceed these
levels. consult the manufacturer for
specific derate procedures.
HOT SURFACE IGNITERS
The hot surface igniter is a silicon
carbide igniter with a ceramic base
and plug in connections. The igniter
only lights the burners. Once the gas
lights, the igniter is de-energized. It
can only be checked for power
during the 34 second warm up period
before the gas valve opens.
FIGURE 116
NORTON IGNITER
TABLE 28
METER TIME
METERTIME IN MINUTES ANO SECONDS FOR NORMAL INPUT RATING OF FURNACES
EQUIPPEDFOR NATURAL OR LP GAS
HEATINGVALUEOF GAS BTU PER CU. FT.
I
900 1000
i
1040 1100 2500 (LP)
MIN. SEC. MIN.
SEC. MIN. SEC. MIN. SEC. MIN. SEC.
INPUT
BTU/HR
45.000
60.000
75.000
90,000
105,000
120.000
METER
SIZE
CU. FT.
ONE
TEN
ONE
TEN
ONE
TEN
ONE
TEN
ONE
TEN
ONE
TEN
NOTE: Handle the igniter with care
as it is easily damaged.
Check. If the furnace doesn't light
and gas does get to the burners,
make the following test. Unplug the
igniter 2-prong connector from the
wiring harness to the furnace control
board prior to conducting this test.
1. Call for heat at the thermostat.
2. Allow the induced draft blower to
operate for 30 seconds.
3. Use a voltmeter to measure the
voltage coming to the igniter at
the 2-prong connector junction
1 12
1
20
1
23
1
12
0
13
20 13
50
I
14
0
54 1
0
1
3
1
9 0
10
0
10 24 11
0
44
0
48
0 50 0
7 12
8 0 8 19 8
0
36
0
40
0
42
0
6
0
6
40
7
0
7
0
31
0 34
0
36 0
5
10
5
40
6 0 6
0
27
0 30 0 31 0
4
30
5 0 5 10 5
Input BTU/HR
=
Heating Value of Gas (BTU/FT
3
J
x 3600
Time
111Seconds (for 1 cu lt'J al Gas
28
40
6
0
53
48
44
20
38
20
33
30
3
33
2
25
2
20
1
16
1
14
1
12
20
20
30
0
0
0
40
40
26
20
15
30
1~-------~
FIGURE 117
IFC 6-PIN PLUG
plug 30 seconds after the
pressure switches close.
4. If there is no voltage, and the
pressure switches are closed:
A. FIRST check for a broken
wire or loose connection,
B. SECOND, check for voltage
at pins 3 and 1 on the
integrated furnace control
board 6-pin plug; do not
disconnect plug from
control board,
C. if there is no voltage there,
replace the control board.
95
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