SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace: (F/G)9MXT
Specifications subject to change without notice.
10 440 04 4321 04
Table 3 (Cont.) Orifice Size and Manifold Pressure (in. w.c.) for Gas Input Rate
SAGLARUTANFOYTIVARGCIFICEPSSAG.GVA
HEATVALUE0.580.600.620.64
AT ALTITUDE Orifice Mnfld Press Orifice Mnfld Press Orifice Mnfld Press Orifice Mnfld Press
(Btu/cu ft) No. High/Low No. High/Low No. High/Low No. High/Low
TWO-STAGE FURNACE
(TABULATED DATA BASED ON 20,000 BTUH HIGH-HEAT / 13,000 BTUH LOW-HEAT PER BURNER,
DERATED 2%/1000 FT (305M) ABOVE SEA LEVEL)
ALTITUDE
RANGE
ft (m)
650 42 3.4 / 1.4 42 3.5 / 1.5 42 3.6 / 1.5 42 3.7 / 1.6
7001 675 43 3.8 / 1.6 42 3.2 / 1.4 42 3.3 / 1.4 42 3.4 / 1.5
(2134) 700 43 3.5 / 1.5 43 3.7 / 1.5 43 3.8 / 1.6 42 3.2 / 1.4
725 44 3.8 / 1.6 43 3.4 / 1.4 43 3.5 / 1.5 43 3.6 / 1.5
750 44 3.5 / 1.5 44 3.7 / 1.5 44 3.8 / 1.6 43 3.4 / 1.4
8000 775 44 3.3 / 1.4 44 3.4 / 1.4 44 3.5 / 1.5 44 3.7 / 1.5
(2438) 800 45 3.8 / 1.6 44 3.2 / 1.4 44 3.3 / 1.4 44 3.4 / 1.4
825 46 3.7 / 1.6 46 3.8 / 1.6 45 3.8 / 1.6 44 3.2 / 1.4
625 42 3.4 / 1.4 42 3.5 / 1.5 42 3.6 / 1.5 42 3.7 / 1.6
8001 650 43 3.8 / 1.6 42 3.2 / 1.4 42 3.3 / 1.4 42 3.4 / 1.4
(2439) 675 43 3.5 / 1.5 43 3.6 / 1.5 43 3.7 / 1.6 42 3.2 / 1.3
700 44 3.7 / 1.6 43 3.4 / 1.4 43 3.5 / 1.5 43 3.6 / 1.5
725 44 3.5 / 1.5 44 3.6 / 1.5 44 3.7 / 1.6 44 3.8 / 1.6
9000 750 44 3.3 / 1.4 44 3.4 / 1.4 44 3.5 / 1.5 44 3.6 / 1.5
(2743) 775 45 3.7 / 1.6 44 3.2 / 1.3 44 3.3 / 1.4 44 3.4 / 1.4
9001 600 42 3.3 / 1.4 42 3.4 / 1.5 42 3.6 / 1.5 42 3.7 / 1.6
(2744) 625 43 3.7 / 1.6 42 3.2 / 1.3 42 3.3 / 1.4 42 3.4 / 1.4
650 43 3.5 / 1.5 43 3.6 / 1.5 43 3.7 / 1.6 43 3.8 / 1.6
675 44 3.7 / 1.6 44 3.8 / 1.6 43 3.4 / 1.4 43 3.5 / 1.5
10000 700 44 3.4 / 1.4 44 3.5 / 1.5 44 3.7 / 1.5 44 3.8 / 1.6
(3048) 725 44 3.2 / 1.3 44 3.3 / 1.4 44 3.4 / 1.4 44 3.5 / 1.5
* Orifice numbers shown in BOLD are factory-installed.
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U.S.A. OnlyU.S.A. Only U.S.A. Only
A11252B
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.
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.
CAUTION
!
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:
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 readings. This is particularly
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.
ELECTRICAL OPERATION HAZARD
Failure to follow this warning could result in personal injury
or death.
Disconnect 115vac electrical power before changing speed
tap.
!
WARNING
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