NOTE:
To repeat component test, turn setup switch SW1-6 OFF,
then back ON.
(1.) Turn Setup DIP switch SW1-6 OFF. Reconnect R lead
to furnace control board, release blower door switch
and re-install blower access door.
4. Operate furnace per instruction on inner door.
5. Verify furnace shut down by lowering thermostat setting
below room temperature.
6. Verify furnace restarts by raising thermostat setting above
room temperature.
Step 3—Adjustments
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.
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.
48.)
Furnace gas input rate on rating plate is for installations at altitudes
up to 2000 ft. Furnace input rate must be within ±2 percent of
furnace rating plate input.
In the U.S.A., the input rating for altitudes above 2,000 ft. must be
reduced by 4 percent for each 1,000 ft. above sea level. In Canada,
input rating must be reduced by 10 percent for altitudes of 2,000
ft. to 4,500 ft. above sea level. For altitudes above 5500 ft., a
field-supplied high altitude pressure switch is required.
1. Determine the correct gas input rate.
In the U.S.:
For installations below 2000 ft., refer to the unit rating plate.
For installations above 2000 ft., multiply the input on the
rating plate by the de-rate multiplier in Table 7 for the correct
input rate.
In Canada:
At installation altitudes from 2000 to 4500 ft, this furnace must be
derated 10 percent by an authorized Gas Conversion Station or
Dealer. To determine correct input rate for altitude, see example
and use 0.90 as derate multiplier factor.
EXAMPLE:
88,000 BTUH INPUT FURNACE INSTALLED AT 4300 FT.
Derate
Furnace Input Rate
Furnace Input Rate
X
Multiplier
=
at Installation
at Sea Level
Factor
Altitude
88,000
X
0.90
=
79,200
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 10 (22,000 Btuh
per burner.) Low NOx models in downflow or horizontal
positions must use Table 11 (21,000 Btuh per burner.)
See input listed on rating plate.
a. Obtain average yearly gas heat value (at installed altitude)
from local gas supplier.
b. Obtain average yearly gas specific gravity from local gas
supplier.
c. Find installation altitude in Table 10 or 11.
d. Find closest natural gas heat value and specific gravity in
Table 10 or 11.
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.
g. Replace orifice with correct size if required by Table 10 or
11. Use only factory-supplied orifices. See EXAMPLE 2.
22,000 Btuh per burner application use Table 10.
EXAMPLE 2: (0–2000 ft altitude)
Heating value = 1000 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 43*
Manifold pressure: 3.7-in. wc for high-heat
1.6-in. wc 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.
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 variable speed furnace control to
ON position. (See Table 6) to lock furnace in low-heat
operation.
f. Manually close blower door switch.
g. Jumper R and W/W1 thermostat connections on control to
start furnace.
h. Remove regulator adjustment cap from low fire gas valve
pressure regulators. (See Fig. 47.) and turn low-heat
adjusting screw (5/64 hex Allen wrench) 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
wc or more than 1.7-in. wc for natural gas. If manifold pressure is
outside this range, change main burner orifices.
i. Install low-fire regulator adjustment cap.
Table 7–Altitude Derate Multipler for U.S.A.
ALTITUDE
(FT)
PERCENT
OF DERATE
DERATE MULTIPLIER
FACTOR*
0–2000
0
1.00
2001–3000
8–12
0.90
3001–4000
12–16
0.86
4001–5000
16–20
0.82
5001–6000
20–24
0.78
6001–7000
24–28
0.74
7001–8000
28–32
0.70
8001–9000
32–36
0.66
9001–10,000
36–40
0.62
* Derate multiplier factors are based on midpoint altitude for altitude range.
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