SERVICE AND TECHNICAL SUPPORT MANUAL
Gas Furnace: N9MSB
Specifications subject to change without notice.
440 04 4413 03
15
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. Always reinstall access doors after
completing service and maintenance.
!
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
, you must revise your orientation to component
location accordingly.
Figure 6
Multipoise Orientations
A93041
Electrical Controls and Wiring
Pressure Switches
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
information and to
for furnace wiring information.
NOTE
: If the polarity is not correct, the STATUS LED on the
control will flash code 10 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
) 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 display will be off when fuse
needs to be replaced.
