28
SERVICING
Induced Draft Blower
Pressure Switch
Pressure Switch
Hose
1/4" Tee
Hose to Induced
Draft Blower Tap
Inclined Manometer
ID Blower Pressure Switch
Negative Pressure Measurement
(80% Upflow Single-Stage Furnace Shown,
Counterflow Similar)
S-311 HIGH ALTITUDE APPLICATION (USA)
The furnace as shipped requires no change to run between
0 - 5500 feet. Do not attempt to increase the firing rate by
changing orifices or increasing the manifold pressure below
5500 feet. This can cause poor combustion and equipment
failure. High altitude installations above 5500 feet may re
-
quire both a pressure switch and an orifice change. These
changes are necessary to compensate for the natural reduc
-
tion in the density of both the gas fuel and the combustion air
at higher altitude.
For installations above 5500 feet, please refer to your dis
-
tributor for required kit(s). Contact the distributor for a tabu
-
lar listing of appropriate manufacturer’s kits for propane gas
and/or high altitude installations. The indicated kits must be
used to insure safe and proper furnace operation. All conver
-
sions must be performed by a qualified installer, or service
agency.
In some areas the gas supplier may artificially derate the
gas in an effort to compensate for the effects of altitude. If
the gas is artificially derated the appropriate orifice size must
be determined based on the BTU/ft3 content of the derated
gas and the altitude. Refer to the National Fuel Gas Code,
NFPA 54/ANSI Z223.1, and information provided by the gas
supplier to determine the proper orifice size.
S-312 CHECKING FOR DELAYED IGNITION
Delayed ignition is a delay in lighting a combustible mixture
of gas and air which has accumulated in the combustion
chamber.
Furnace design makes this extremely unlikely unless safety
controls have been by-passed or tampered with. Never by-
pass or alter furnace controls.
If delayed ignition should occur, the following should be
checked:
1. Improper gas pressure - adjust to proper pressure
(See
S-307 CHECKING GAS PRESSURE
).
2. Improper burner positioning - burners should be in
locating slots, level front to rear and left to right.
3. Carry over (lighter tube or cross lighter) obstructed -
clean.
4.
Main burner orifice(s) deformed, or out of alignment
to burner - replace.
S-313 CHECKING INTEGRATED IGNITION
CONTROL BOARDS
NOTE: Failure to earth ground the furnace, revers
-
ing the neutral and hot wire connection to the line
(polarity), or a high resistance connection in the
neutral line may cause the control to lockout due
to failure to sense flame.
WARNING
To avoid the risk of electrical shock, wiring to the unit
must be properly polarized and grounded. Disconnect power
before performing service listed below.
The ground wire must run from the furnace all the way back
to the electrical panel. Proper grounding can be confirmed
by disconnecting the electrical power and measuring resis-
tance between the neutral (white) connection and the burner
closest to the flame sensor. Resistance should be less than
10 ohms.
The ignition control is a combination electronic and electro-
mechanical device and is not field repairable. Complete unit
must be replaced.
