ICP G9MAE0601714A Service And Technical Support Manual page 6

SERVICE AND TECHNICAL SUPPORT MANUAL
To do this:
1. Obtain average heat value (at installed altitude) from
local gas supplier.
2. Obtain average specific gravity from local gas supplier.
3. Find installation altitude range for your installation in the
manifold pressure tables. See Table 4 for the 20,000
Btuh Max−Heat/8,000/Btuh Min−Heat per burner models
or Table 5 for model *9MAE0602120 only (20,200 Btuh
Max−Heat/8,000 Btuh Min−Heat per burner).
4. Find closest natural gas heat value and specific gravity in
Table 4 or Table 5 depending on furnace gas input rate.
5. Follow heat value and specific gravity lines to point of
intersection to find orifice size and maximum and
minimum manifold pressure settings for proper operation.
6. Check and verify burner orifice size in furnace. Never
assume orifice size. NEVER ASSUME ORIFICE SIZE.
ALWAYS CHECK AND VERIFY.
NOTICE
If orifice hole appears damaged or it is suspected to have been
redrilled, check orifice hole with a numbered drill bit of correct
size. Never redrill an orifice. A burr−free and squarely aligned
orifice hole is essential for proper flame characteristics.
7. Replace orifice with correct size, if required by Table 4
or Table 5 depending on furnace gas input rate. Use only
factory−supplied orifices. See EXAMPLE 1.
EXAMPLE 1:
(See Table 4)
0 - 2000 ft. (0 - 609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
(Furnace is shipped with No. 44 orifices. In this example, all
main burner orifices are the correct size and do not need to be
changed to obtain proper input rate.)
Manifold pressure: 3.4-in. w.c. (847 Pa) for Maximum heat,
.55-in. w.c. (349 Pa) for Minimum heat
NOTE: To convert gas manifold Table pressures to Pascals,
multiply the in.w.c. value by 249.1 Pa/in. w.c. (1 in. wc. = 249.1
Pa).
Table 1 Altitude Derate Multiplier for U.S.A.
ALTITUDE PERCENT
FT. (M) OF DERATE
0–2000
0
(0−610)
2001–3000
4−6
(610−914)
3001–4000
6−8
(914−1219)
4001–5000
8−10
(1219−1524)
5001–6000
10−12
(1524−1829)
6001–7000
12−14
(1829−2134)
7001–8000
14−16
(2134−2438)
8001–9000
16−18
(2438−2743)
9001–10,000
18−20
(2743−3048)
* Derate multiplier factors are based on midpoint altitude for altitude range.
6
DERATE MULTIPLIER
FACTOR*
1.00
0.95
0.93
0.91
0.89
0.87
0.85
0.83
0.81
Specifications subject to change without notice.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (610 to
1372 M), use USA altitudes of 2001 to 3000 ft. (610 to 914
M).
Check Inlet Gas Pressure
The inlet gas pressure must be checked with the furnace
operating in maximum heat. This is necessary to make sure the
inlet gas pressure does not fall below the minimum pressure of
4.5−in. w.c. for natural gas. The maximum inlet gas pressure is
13.6−in. w.c. If the inlet pressure is too low, you will not be able
to adjust the manifold pressure to obtain the proper input rate.
To check the inlet gas pressure:
1. Make sure the gas supply is turned off to the furnace and
at the electric switch on the gas valve.
2. Remove the 1/8 inch NPT plug from the inlet pressure
tap on the gas valve.
3. Connect a manometer to the inlet pressure tap on gas
valve.
4. Turn on furnace power supply.
5. Turn gas supply manual shutoff valve to ON position.
6. Turn furnace gas valve switch to ON position.
7. Jumper the R to W/W1 and W2 thermostat connections
at the furnace control board.
8. When main burners ignite, confirm inlet gas pressure is
Between 4.5−in. w.c. and 13.6−in. w.c.
9. Remove jumper across thermostat connections to
terminate call for heat. Wait until the blower off delay is
completed.
10. Turn furnace gas valve electric switch to OFF position.
11. Turn gas supply manual shutoff valve to OFF position.
12. Turn off furnace power supply.
13. Remove manometer from the inlet pressure tap of the
gas valve.
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal injury,
death, and/or property damage.
Re−install manifold pressure tap plug in gas valve to
prevent gas leak.
14. Apply pipe dope sparingly to end of inlet gas pipe plug
and re−install in the gas valve.
Adjust Manifold Pressure−Maximum Heat
The modulating furnace manifold pressure is set at two points.
The first point is Maximum Heat.
The second point is Minimum Heat. Do not adjust Intermediate
Heat manifold pressure. Intermediate Heat manifold pressure is
checked as part of the temperature rise, but is not adjustable.
Always adjust Maximum Heat first, then Minimum Heat.
NOTICE
DO NOT set maximum heat manifold pressure less than 3.2−in.
w.c. (947 Pa) for natural gas. If required manifold pressure is
outside this range, change main burner orifices to obtain
manifold pressure in this range.
To adjust manifold pressure to obtain input rate for Maximum
Heat:
1. Make sure the gas supply is turned off to the furnace and
at the electric switch on the gas valve.
Gas Furnace: (F/G)9MAE
440 04 4700 00