73
SERVICE AND MAINTENANCE
PROCEDURES
Untrained personnel can perform basic maintenance functions such
as cleaning and replacing air filters. All other operations must be
performed by trained service personnel. A qualified service person
should inspect the furnace once a year.
FIRE, INJURY OR DEATH HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
The ability to properly perform maintenance on this
equipment requires certain knowledge, mechanical skills,
tools, and equipment. If you do not possess these, do not
attempt to perform any service and maintenance on this
equipment other than those procedures recommended in the
Owner’s Manual.
!
WARNING
ENVIRONMENTAL HAZARD
Failure to follow this caution may result in environmental
pollution.
Remove and recycle all components or materials (i.e. oil,
refrigerant, control board, etc.) before unit final disposal.
CAUTION
!
ELECTRICAL SHOCK, FIRE OR EXPLOSION
HAZARD
Failure to follow this warning could result in personal
injury or death, or property damage.
Before installing, modifying, or servicing system, main
electrical disconnect switch must be in the OFF position and
install a lockout tag. There may be more than one
disconnect switch. Lock out and tag switch with a suitable
warning label. Verify proper operation after servicing.
!
WARNING
ELECTRICAL OPERATION HAZARD
Failure to follow this caution may result in improper
furnace operation or failure of furnace.
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and dangerous
operation.
CAUTION
!
General
These instructions are written as if the furnace is installed in an
upflow application. An upflow furnace application is where the
blower is located below the combustion and controls section of the
furnace, and conditioned air is discharged upward. Since this
furnace can be installed in any of the 4 positions shown in Fig. 2,
you must revise your orientation to component location
accordingly.
Electrical Controls and Wiring
Each pressure switch is labeled with the reference location (noted
as “COLLECTOR BOX
−
LPS” or “HOUSING
−
HPS” on the
switch). The nominal break point of each switch is shown on the
label below the reference location in inches of water column,
“W.C.” The maximum and minimum break point of the switch is
+/
−
0.05 inches of water column from the nominal break point of
the switch. The maximum make point of the switch is 0.10 inches
of water above the maximum break point of the switch.
Example
: Nominal break point on pressure switch is 0.68
−
in.
W.C. The minimum break point of the switch is 0.63
−
in. W.C.
The maximum break point of the switch is 0.73
−
in. W.C. The
maximum make point of the switch is 0.83
−
in. W.C.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury
or death.
There may be more than one electrical supply to the furnace.
Check accessories and cooling unit for additional electrical
supplies that must be shut off during furnace servicing. Lock
out and tag switch with a suitable warning label.
!
WARNING
The electrical ground and polarity for 115
−
v wiring must be
properly maintained. Refer to Fig. 39 for field wiring information
and to Fig. 73 for furnace wiring information.
NOTE
: If the polarity is not correct, the STATUS LED on the
control will flash rapidly and prevent the furnace from heating. The
control system also requires an earth ground for proper operation
of the control and flame
−
sensing electrode.
The 24
−
v circuit contains an automotive
−
type, 3
−
amp. fuse located
on the control. See Fig. 40. Any shorts of the 24
−
v wiring during
installation, service, or maintenance will cause this fuse to blow. If
fuse replacement is required, use ONLY a 3
−
amp. fuse. The control
LED will display status code 24 when fuse needs to be replaced.
Troubleshooting
Refer to the service label. See Fig. 64.
The Troubleshooting Guide can be a useful tool in isolating
furnace operation problems. Beginning with the word “Start,”
answer each question and follow the appropriate arrow to the next
item. See Fig. 72.
The Guide will help to identify the problem or failed component.
After replacing any component, verify correct operation sequence.
Proper instrumentation is required to service electrical controls.
The control in this furnace is equipped with a Status Code LED
(Light
−
Emitting Diode) to aid in installation, servicing, and
troubleshooting. Status codes can be viewed at the indicator in
blower door. The amber furnace control LED is either ON
continuously, rapid flashing, or a code composed of 2 digits. The
first digit is the number of short flashes, the second digit is the
number of long flashes.
For an explanation of status codes, refer to service label located on
control door or Fig. 64, and the troubleshooting guide which can
be obtained from your distributor.
Retrieving Stored Fault Codes
NOTE
: Fault codes cannot be retrieved if a thermostat signal
(24-v on W, Y, G, etc.) is present, or if any delays such as blower
off-delays are active.
The stored status codes will NOT be erased from the control
memory when 115- or 24-v power is interrupted. See the Service
Label (Fig. 64) for more information. The most recent fault code
may be retrieved as follows:
1. Leave 115-v power connected to furnace.
2. Observe the status LED through the blower door (the lower
door on upflow applications) indicator. Refer to the Service
Label (Fig. 64) to interpret the LED.
3. Remove the Main/Control door (the upper door on upflow
installations).
4. BRIEFLY disconnect and reconnect ONE of the main limit
wires.
912S
