18
IM 685-1
Models 020 thru 025 (see Figure 14)
1. To gain access to the inside of the combustion chamber,
detach the burner from the furnace and set it on the floor
of the vestibule (see Figure 14, Item (3)). The burner is
attached to the furnace studs with four nuts. Conduit
lengths allows this movement of the burner without dis-
connecting wiring. The union on the gas line must be
opened.
2. Remove the flue box front wrap (1) .
3. Remove and clean the turbulator (2) from each tube and
clean the flue box.
4. Clean each tube with a 2
½
" round flue brush.
5. Remove the brushings and if required clean the combus-
tion chamber and header through the burner mounting
tube.
6. Reinstall the burner.
7. Reinstall a turbulator in each tube approximately flush
with the tube end, locking them in place with the wedge
clips on each turbulator.
8. Reinstall flue box front wrap (1).
Figure 14. Models 020 thru 025 Heat Exchanger
Leakage Symptoms
1.
Odor
- Odors in the building are usually being brought in
through the outdoor air intakes and do not indicate leak-
age from the furnace. Check for down draft conditions
and check the location of the flue exhausts of other equip-
ment that may be pulled into the outdoor air intake. A
major and obvious furnace rupture can be a source of
odor. In general, small leaks in a furnace will not be a
source of odor or danger because the pressure created by
the supply fan is greater than the pressure inside the fur-
nace. Therefore when the supply fan is operating, leakage
will be
into
the furnace, not
out of
the furnace and into
the air stream. If the control system is such that the fur-
nace comes on and warms up the heat exchanger before
the supply air fan comes on, and there is odor when the
supply fan first comes on, this could be caused by leak-
age. During the time the furnace is on and the supply fan
is off the leakage would be out off the furnace and then
when the supply fan came on it would blow those prod-
ucts of combustion into the supply duct.
2.
Low CO
2
Readings
- Low CO
2
readings that cannot be
corrected can be caused by air leaking into the heat
exchanger and diluting the flue gas. If this is suspected,
take two consecutive CO
2
readings, one with the supply
fan running and one with the supply fan off. If the CO
2
increases with the supply fan off, it could indicate leak-
age. Note that CO
2
samples must be taken from inside a
tube, not just from inside the flue box.
Checking for Leaks
1. Open up the rear casing panel while the unit is shut off
and visually inspect the heat exchanger.
2. Visually inspect the heat exchanger while the burner is
operating, looking for light coming through holes. The
burner should only be operated for a few minutes with the
supply fan off, and take necessary safety precautions
around the hot heat exchanger.
3. Perform consecutive CO
2
tests with supply fan off and
on. See Item 2 under "Leakage Symptoms."
4.
Smoke Bomb Test -
Cover the flue box openings, open
the rear casing panel so the heat exchanger is accessible,
toss a smoke bomb into the heat exchanger through the
rear inspection port, replace the port cover, and with a
bright light look for smoke leaking through the heat
exchanger. Remove the remains of the smoke bomb and
uncover the flue box openings before attempting to oper-
ate the furnace.
Note:
In most cases small leaks in the heat exchanger are not
a source of danger. Because the pressure created by the sup-
ply fan is greater than that inside the heat exchanger, the
leakage will be
into
the heat exchanger, not
out of
the heat
exchanger and into the airstream.
Causes of Failures
1.
Improper Application -
The furnace rating plate speci-
fies a "Minimum Airflow CFM." The furnace must not be
operated when airflow is below this minimum cfm. If the
furnace is being used on a variable air volume system, the
control system must be such that the furnace will not
operate when the supply fan cfm has fallen below this
minimum specified cfm. The furnace rating plate also
specifies a "Maximum MBH Input" which must not be
exceeded. See "Verify Input Rate."
2.
Control Failure -
The limit control does not function
properly to shut off the burner when the heat exchanger
temperature becomes excessive. In most situations, a
properly controlled unit will never even require the limit
control to shut off the unit. The limit control should be a
backup control and a problem attributed to a limit failure
would generally indicate a control problem in addition to
the limit failure.
3
2 1/2 Round Flue Brush With 4 Foot Handle
2
1
Condensate Drain
Wind Deflector
Summary of Contents for SuperMod IM-685-1
Page 27: ...IM 685 1 27 Notes ...
