FIGURE 21
STATIC PRESSURE TEST
Page 21
B−Temperature Rise
Temperature rise for G40DF(X) units depends on unit in-
put, blower speed, blower horsepower and static pressure
as marked on the unit rating plate. The blower speed must
be set for unit operation within the range of TEMP. RISE
°
F" listed on the unit rating plate.
To Measure Temperature Rise:
1 − Place plenum thermometers in the supply and return air
plenums. Locate supply air thermometer in the first hori-
zontal run of the plenum where it will not pick up radiant
heat from the heat exchanger.
2 − Set thermostat to highest setting.
3 − After plenum thermometers have reached their high-
est and steadiest readings, subtract the two readings.
The difference should be in the range listed on the unit
rating plate.
If the temperature is too low, decrease blower speed.
If temperature is too high, first check the firing rate.
Provided the firing rate is acceptable, increase blower
speed to reduce temperature. To change blower speed
taps see the Blower Speed Taps section in this manual.
C−External Static Pressure
1 − Tap locations shown in figure 21.
2 − Punch a 1/4" diameter hole
in supply and return air ple-
nums. Insert manometer
hose flush with inside edge
of hole or insulation. Seal
around the hose with perma-
gum. Connect the zero end
of the manometer to the dis-
charge (supply) side of the system. On ducted sys-
tems, connect the other end of manometer to the return
duct as above. For systems with non−ducted returns,
leave the other end of the manometer open to the at-
mosphere.
3 − With only the blower motor running and the evaporator
coil dry, observe the manometer reading. Adjust blow-
er motor speed to deliver the air desired according to
the job requirements.
4 − External static pressure drop must not be more than
0.5" W.C.
5 − Seal around the hole when the check is complete.
D−Blower Speed Taps
Blower speed tap changes are made on the SureLight con-
trol board. See figures 3, 5 and 6. For controls 56L84,
10M93 and 32M88 the heating tap is connected to the
HEAT−H" terminal and the cooling tap is connected to the
COOL−H" terminal. On controls 69M08 and 78M47 the
heating tap is connected to the HEAT" terminal and the
cooling tap is connected to t he COOL" terminal. On all
units the continuous blower tap is the same as the heating
tap and unused taps must be secured on two dummy termi-
nals labeled "PARK.
VI−MAINTENANCE
At the beginning of each heating season, the system
should be checked as follows:
A−Filters
All G40DF(X) filters are installed external to the unit. Filters
should be inspected monthly. Clean or replace the filters
when necessary to ensure that the furnace operates prop-
erly. Replacement filters must be rated for high velocity air-
flow.
B− Heat Exchanger and Burners
Cleaning the Heat Exchanger and Burners
NOTE−Use papers or protective covering in front of fur-
nace while cleaning furnace.
Cleaning the heat exchanger requires a steel spring
snake," a reversible drill and a vacuum cleaner. The steel
spring snake may be constructed by purchasing a 4 ft. long
by 1/4" diameter steel wire cable and a 1/4" diameter wire
brush. These items are available at a hardware store. In-
sert wire end of brush into the open end of the spring cable.
Crimp the cable around the brush so that the brush is se-
cured and will not come off during cleaning. Attach the oth-
er end of the cable to the reversible drill to complete the tool
for cleaning the heat exchanger. See figure 1 for parts ar-
rangement when disassembling furnace.
1 − Turn off both electrical and gas power supplies to fur-
nace.
2 − Remove flue pipe and top cap from unit. Mark and dis-
connect wiring from prove switch and combustion air
inducer.
FIGURE 22
G40DF(X) BURNER & HEAT
EXCHANGER REMOVAL
HEAT EXCHANGER
BURNER BOX ASSEMBLY
NOX INSERT