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Adjustments
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result
in excess overfire and heat exchanger failures.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT redrill orifices. Improper drilling (burrs,
out- -of- -round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. This can result in flame
impingement of heat exchangers, causing failures. (See Fig.
50.)
Furnace gas input rate on rating plate is for installations at
altitudes up to 2000 Ft. (610 M). Furnace input rate must be
within +/- -2 percent of furnace rating plate input. For altitudes
above 5500 Ft. (1676 M), a field- -supplied high altitude pressure
switch is required.
1. Determine the correct gas input rate.
The input rating for altitudes above 2,000 ft. (610 M) must
be reduced by 4 percent for each 1,000 ft. (305 M) above
sea level.
For installations below 2000 Ft. (610 M), refer to the unit
rating plate. For installations above 2000 Ft. (610 M),
multiply the input on the rating plate by the de- -rate multi-
plier in Table 11 for the correct input rate.
2. Determine the correct orifice and manifold pressure adjust-
ment. All models in all positions except Low NOx models
in downflow and horizontal positions use Table 14
(22,000 Btuh per burner.) Low NOx models in downflow
or horizontal positions must use Table 15 (21,000 Btuh
per burner.) See input listed on rating plate.
a. Obtain average yearly gas heat value (at installed alti-
tude) from local gas supplier.
b. Obtain average yearly gas specific gravity from local
gas supplier.
c. Find installation altitude in Table 14 or 15.
d. Find closest natural gas heat value and specific gravity
in Table 14 or 15.
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and low- -and high- -heat
manifold pressure settings for proper operation.
f. Check and verify burner orifice size in furnace.
NEVER ASSUME ORIFICE SIZE. ALWAYS
CHECK AND VERIFY.
NOTE: 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.
g. Replace orifice with correct size, if required by Table
14 or 15. Use only factory- -supplied orifices. See
EXAMPLE 1.
Table 11 – Altitude Derate Multiplier for U.S.A.
ALTITUDE
PERCENT
FT. (M)
OF DERATE
0–2000
(0--- 610)
2001–3000
(610--- 914)
3001–4000
(914--- 1219)
4001–5000
(1219--- 1524)
5001–6000
1524--- 1829)
6001–7000
(1829--- 2134)
7001–8000
(2134--- 2438)
8001–9000
(2438--- 2743)
9001–10,000
(2743--- 3048)
Table 12 – Blower Off Delay Setup Switch
DESIRED HEATING MODE
BLOWER OFF DELAY (SEC.)
90
120
150
180
EXAMPLE 1: 0–2000 ft. (0- -610 M) altitude
For 22,000 Btuh per burner application use Table 14.
Heating value = 1000 Btuh/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 43*
Manifold pressure: 3.7- -In. W.C. for high- -heat
1.6- -In. W.C. for low- -heat
* Furnace is shipped with No. 43 orifices. In this example all
main burner orifices are the correct size and do
not need to be changed to obtain proper input rate.
3. Adjust manifold pressure to obtain low fire input rate. (See
Fig. 49.)
a. Turn gas valve ON/OFF switch to OFF.
b. Remove manifold pressure tap plug from gas valve.
c. Connect a water column manometer or similar device
to manifold pressure tap.
d. Turn gas valve ON/OFF switch to ON.
e. Move setup SW1—2 on furnace control to ON posi-
tion to lock furnace in low- -heat operation. (See Table
10 and Fig. 24.)
f. Manually close blower door switch.
g. Jumper R and W/W1 thermostat connections on con-
trol to start furnace. (See Fig. 24.)
h. Remove regulator adjustment cap from low heat gas
valve pressure regulator (See Fig. 49.) and turn low- -
heat adjusting screw (3/16 or smaller flat- -tipped
screwdriver) counterclockwise (out) to decrease input
rate or clockwise (in) to increase input rate.
NOTE:
DO NOT set low- -heat manifold pressure less than
1.4- -In. W.C. or more than 1.7- -In. W.C. for natural gas. If
manifold pressure is outside this range, change main burner
orifices.
i. Install low- -heat regulator adjustment cap.
39
DERATE MULTIPLIER
FACTOR*
0
1.00
8–12
0.90
12–16
0.86
16–20
0.82
20–24
0.78
24–28
0.74
28–32
0.70
32–36
0.66
36–40
0.62
SETUP SWITCH
(SW --- 7 AND --- 8)
POSITION
SW1--- 7
SW1--- 8
OFF
ON
OFF
ON
OFF
OFF
ON
ON
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