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SERVICE AND TECHNICAL SUPPORT MANUAL
Table 3 (Cont.)
Orifice Size and Manifold Pressure (in. w.c.) for Gas Input Rate
(TABULATED DATA BASED ON 20,000 BTUH HIGH-HEAT / 13,000 BTUH LOW-HEAT PER BURNER,
ALTITUDE
A
RANGE
HEAT VALUE
AT ALTITUDE
ft (m)
7001
(2134)
to
8000
(2438)
8001
(2439)
to
9000
(2743)
9001
(2744)
to
10000
(3048)
* Orifice numbers shown in BOLD are factory-installed.
Adjust Temperature Rise
NOTE: Blower door must be installed when taking temperature
rise reading. Leaving blower door off will result in incorrect
temperature measurements, due to possible changes in duct
static pressure and airflow.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in:
S
Overheating the heat exchangers or condensing
flue gases in heat exchanger areas not designed
for condensate
S
Shortened furnace life
S
Component damage
Temperature rise must be within limits specified on furnace
rating plate. Recommended operation is at midpoint of rise
range or slightly above.
Place SW−1 (TT) in ON position. Jumper R to W/W1 and W2 to
check high−heat temperature rise. To check low−heat
temperature rise, remove jumper to W2. Determine air
temperature rise for both high and low−heat. Do not exceed
temperature rise ranges specified on unit rating plate for high
and low−heat.
This furnace must operate within the temperature rise ranges
specified on the furnace rating plate. Determine the air
temperature as follows:
10
TWO-STAGE FURNACE
DERATED 2%/1000 FT (305M) ABOVE SEA LEVEL)
V
G
.
G
A
S
0.58
Orifice Mnfld Press Orifice Mnfld Press Orifice Mnfld Press Orifice Mnfld Press
(Btu/cu ft)
No.
High/Low
650
42
3.4 / 1.4
675
43
3.8 / 1.6
700
43
3.5 / 1.5
725
44
3.8 / 1.6
750
44
3.5 / 1.5
775
44
3.3 / 1.4
800
45
3.8 / 1.6
825
46
3.7 / 1.6
625
42
3.4 / 1.4
650
43
3.8 / 1.6
675
43
3.5 / 1.5
700
44
3.7 / 1.6
725
44
3.5 / 1.5
750
44
3.3 / 1.4
775
45
3.7 / 1.6
600
42
3.3 / 1.4
625
43
3.7 / 1.6
650
43
3.5 / 1.5
675
44
3.7 / 1.6
700
44
3.4 / 1.4
725
44
3.2 / 1.3
Specifications subject to change without notice.
S
P
E
C
F I
C I
G
R
A
V
T I
Y
O
F
N
A
T
U
R
0.60
0.62
No.
High/Low
No.
High/Low
42
3.5 / 1.5
42
3.6 / 1.5
42
3.2 / 1.4
42
3.3 / 1.4
43
3.7 / 1.5
43
3.8 / 1.6
43
3.4 / 1.4
43
3.5 / 1.5
44
3.7 / 1.5
44
3.8 / 1.6
44
3.4 / 1.4
44
3.5 / 1.5
44
3.2 / 1.4
44
3.3 / 1.4
46
3.8 / 1.6
45
3.8 / 1.6
42
3.5 / 1.5
42
3.6 / 1.5
42
3.2 / 1.4
42
3.3 / 1.4
43
3.6 / 1.5
43
3.7 / 1.6
43
3.4 / 1.4
43
3.5 / 1.5
44
3.6 / 1.5
44
3.7 / 1.6
44
3.4 / 1.4
44
3.5 / 1.5
44
3.2 / 1.3
44
3.3 / 1.4
42
3.4 / 1.5
42
3.6 / 1.5
42
3.2 / 1.3
42
3.3 / 1.4
43
3.6 / 1.5
43
3.7 / 1.6
44
3.8 / 1.6
43
3.4 / 1.4
44
3.5 / 1.5
44
3.7 / 1.5
44
3.3 / 1.4
44
3.4 / 1.4
1. Place duct thermometers in return and supply ducts as
close to furnace as possible. Be sure thermometers do
not "see" heat exchangers so that radiant heat does not
affect
thermometer
important with straight run ducts.
2. When thermometer readings stabilize, subtract return−air
temperature from supply−air temperature to determine
temperature rise.
If the temperature rise is outside this range, check the
following:
1. Gas input for low and high heat operation.
2. Derate for altitude if applicable.
3. Return and supply ducts for excessive restrictions
causing static pressures greater than 0.50−in. w.c. (125
Pa)
4. Adjust temperature rise by adjusting blower speed.
S
Increase blower speed to reduce temperature rise.
S
Decrease blower speed to increase temperature rise.
WARNING
!
ELECTRICAL OPERATION HAZARD
Failure to follow this warning could result in personal injury
or death.
Disconnect 115vac electrical power before changing speed
tap.
Gas Furnace: (F/G)9MXT
A
L
G
A
S
0.64
No.
High/Low
42
3.7 / 1.6
42
3.4 / 1.5
42
3.2 / 1.4
43
3.6 / 1.5
43
3.4 / 1.4
44
3.7 / 1.5
44
3.4 / 1.4
44
3.2 / 1.4
42
3.7 / 1.6
42
3.4 / 1.4
42
3.2 / 1.3
43
3.6 / 1.5
44
3.8 / 1.6
44
3.6 / 1.5
44
3.4 / 1.4
42
3.7 / 1.6
42
3.4 / 1.4
43
3.8 / 1.6
43
3.5 / 1.5
44
3.8 / 1.6
44
3.5 / 1.5
readings.
This
is
particularly
440 04 4321 08
A11252B
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