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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 ignition control
board. See figures 5 and 8. On G40DF−1 through −8 units,
the heating tap is connected to the HEAT−H" terminal and
the cooling tap is connected to the COOL−H" terminal. On
G40UHF−8 and later units, 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 se-
cured on two dummy terminals labeled "PARK. To change
out existing speed tap, turn off power and switch out speed
tap with tap connected to PARK". See blower speed tap
table on unit diagram for motor tap colors for each speed.
VI−MAINTENANCE
At the beginning of each heating season, the system
should be checked as follows:
A−Filters
All G40UH(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 23
G40UH(X) BURNER & HEAT
EXCHANGER REMOVAL
HEAT EXCHANGER
BURNER BOX ASSEMBLY
3 − Remove four screws securing the combustion air induc-
er. Carefully remove the combustion air inducer and
prove switch together as a unit to avoid damaging blow-
er gasket. If gasket is damaged, it must be replaced to
prevent leakage.
4 − Remove collector box located behind combustion air
inducer. Care must be taken to avoid damaging the col-
lector box gasket. If the gasket is damaged it must be
replaced to prevent leakage.
5 − Mark then disconnect wires from gas valve and rollout
switch.
6 − Disconnect gas supply piping. Remove six screws se-
curing the burner manifold assembly to the lower vesti-
bule panel and remove the assembly from the unit.
NO
x
units only: remove screws holding NO
x
inserts.
Carefully remove inserts from each heat exchanger
clam. See figure 24.
FIGURE 24
NOx INSERTS
NOX UNITS ONLY
