Service manual

035-20647-001 Rev. A (1004)
4 Unitary Products Group
The blower can be serviced/removed from the inside blower access
panel. In order to facilitate this process the combustion air pipe inside
the furnace has a 2” diameter rubber sleeve. The combustion air pipe
inside the furnace is a two-pipe combination coupled together with this
rubber sleeve. A similar 2” coupling provided loose with the furnace,
should be used on top of the furnace to couple the combustion air pipe
sticking through the casing top, with the combustion air piping. When
the clamps on both of these rubber couplings are loosened, the cou-
plings can be slid up or down the combustion air pipe. This will allow the
small combustion air pipe in front of the blower housing to be removed
easily. After the combustion air pipe is removed, it is easy to remove the
inside blower access panel by pushing it up, against a spring. Blower is
now ready to be serviced through the opening.
If the blower has to be removed through the inside blower access panel,
then the top flange, blower door switch and bottom flange will also have
to be removed.
Air Filters
The filters should be checked every 3 months. On new construction,
check the filters every week for the first four weeks and every three
weeks after that, especially if the indoor fan is running continuously.
When replacing the filter(s), refer to Table 1 to be sure you install the
right size filter for your furnace. Dirty filters greatly restrict the flow of air
and may cause damage to the moving parts of the furnace. If the filters
become clogged the heat exchangers and blower motor could overheat
resulting in a potentially dangerous situation.
Never operate your furnace without a suitable air filter.
Use the following procedure to determine the filter size.
1. Measure the furnace width and use that measurement to deter-
mine the cabinet width.
• A 14-1/2” wide cabinet is an “A” cabinet.
• A 17-1/2” wide cabinet is an “B” cabinet.
• A 21” wide cabinet is an “C” cabinet.
• A 24-1/2” wide cabinet is an “D” cabinet.
2. Locate the cabinet size on Table 1 then determine whether you
have a bottom or side return air duct using the following method.
a. If the return air filter is on the left or right side of the furnace it
is a side return
b. If the air filter is on the bottom of the furnace then you have a
bottom return.
C. If the air filters are on the bottom and the side of the furnace
then you have a bottom and side return. You must replace
both air filters. Table 1 will indicate 2 filters by using brackets
with the number two (2).
D. If the air filters are on both sides of the furnace then you have
a two sided return. You must replace both air filters. Table 1
will indicate 2 filters by using brackets with the number two
(2).
3. After you determine the cabinet size and what return configuration
you have, look up the recommended filter size from Table 1.
Removing Filters
Most downflow furnaces have their filters located on the top of the fur-
nace in an external filter rack. To check filters you should:
1. Follow the instructions to turn off the appliance before servicing.
2. Filters are installed in the return air plenum above the blower
assembly. An “A” frame assembly supports the filters. Lift the filter
slightly and remove for service.
3. Follow the instructions “HOW TO CLEAN YOUR FURNACE’S FIL-
TER”.
4. Reverse the procedure to reinstall filters.
5. Follow the operating instructions to place appliance in operation.
Externally Mounted Air Filters
Some installations may have the air filter in a rack attached to the cas-
ing of the furnace or placed in the return air duct. You can gain access
to the filter by pulling on the door or unscrewing the retaining screw,
then slide the filter(s) out of its channel. Replace throw away filter(s)
with the same size new filter(s). Throw away filter(s) may be replaced
with cleanable filter(s) at this time. Cleanable filter(s) may be cleaned as
described in the manufacturer instructions or as described below and
then re-installed.
How to Clean your Filter
High-velocity filters may be cleaned with a vacuum cleaner or washed
with a garden hose. Be sure to shake off excess water and allow filter to
completely dry before re-installing the filter.
To replace the filter after cleaning you must do the following:
1. Slide filter into place.
2. Snap the door on or place the door in position and tighten the
retaining screws, if provided.
3. Make sure the door is secure to the end of the filter rack.
4. For filter grilles, place the filter into the grilles, close the grille cover
and tighten the retaining screw.
Every time the filters are changed the following items should be visually
inspected:
• Check combustion air and vent pipe for blockage or leakage.
• Check all components to be sure they are in good condition and
that there are no obvious signs of deterioration.
• Check the drain lines to make sure there are no cracks or leaks.
• Check for dirt or lint on any surfaces or on components. Do not try
to clean any of the surfaces or components. Cleaning of the fur-
nace and its components must be done by a qualified service pro-
fessional.
If, during the inspection of your furnace, you find any of the following
conditions:
• Excessive amounts of dust and lint on components.
• Damaged or deteriorated components or surfaces.
• Leaks or blockage in the vent pipe passages.
• Water on any surface inside or outside of the furnace.
Make sure you DO NOT move the clip-on weight on the
indoor fan wheel when cleaning the wheel. This weight is
used to balance the wheel. Moving the weight will cause
the fan wheel to vibrate.
FIGURE 6: Filter Rack Assembly and Attachment
FILTER RACK
(factory supplied with some furnaces)
RACK AND FILTERS SECURED
INSIDE BLOWER SECTION
FOR SHIPMENT
DUCTWORK
FILTERS
BRANCH
DUCTS
FH
CROSS SECTION A-A
(with Plenum and filters)
FILTER
RACK
NOTE: FILTER ACCESS THROUGH
DUCTWORK MUST BE PROVIDED
FOR REMOVAL AND CLEANING
CASING SIZE
DIMENSION FH
16-1/4”
22-1/4”
26-1/4”
12-3/4”
11”
8-1/4”