36
Gas
Rate
Range
Nominal
High Stage 3.2 to 3.8" w.c. 3.5" w.c.
Low Stage 1.6 to 2.2" w.c. 1.9" w.c.
Manifold Gas Pressure
Natural Gas
WARNING
HIGH VOLTAGE
Disconnect ALL electrical power and shut off
gas supply before servicing or installing this
unit. Multiple power sources may be present.
Failure to do so may cause property damage,
personal injury or death.
WARNING
HIGH VOLTAGE
Disconnect ALL electrical power and shut off gas supply
before servicing or installing.
Gas
Rate
Range
Nominal
High Stage 9.7 to 10.3" w.c. 10.0" w.c.
Low Stage 5.7 to 6.3" w.c. 6.0" w.c.
Propane Gas
Manifold Gas Pressure
S-308A Checking Hot Surface Ignitor
120V Silicon Nitride Igniter - Daikin Brand model furnaces
use a 120V silicon nitride igniter for ignition. The normal
operating temperature is approximately 2156°F - 2678°F.
At room temperature the igniter ohm reading should be
from 37-68 ohms.
1. Place unit in heating cycle, measure current draw of
ignitor during preheat cycle.
The steady state current at 120V is 0.37 to 0.68
amps.
2. After checking and/or replacing of hot surface ignitor,
reinstall burner compartment door and verify proper
unit operation.
S-309 Checking For Flashback
Flashback will also cause burning in the burner venturi, but
is caused by the burning speed being greater than the gas-
air flow velocity coming from a burner port.
Flashback may occur at the moment of ignition, after a
burner heats up or when the burner turns off. The latter is
known as extinction pop.
Since the end results of flashback and delayed ignition
can be the same (burning in the burner venturi) a definite
attempt should be made to determine which has occurred.
If flashback should occur, check for the following:
1. Improper gas pressure - adjust to proper pressure
(See S-307
CHECKING GAS PRESSURE
).
2. Check burner for proper alignment and/or replace
burner.
3. Improper orifice size - check orifice for obstruction.
S-310 Checking Pressure Switch
The pressure control is a safety device to prevent the
combustion cycle from occurring with inadequate venting
caused by a restricted or blocked vent pipe. In addition
to the inducer pressure switch, S model furnaces have
a “front cover pressure switch” wired in series with the
gas valve. This pressure switch keeps the gas valve
from opening in the event of condensate backing up in
the secondary heat exchanger. This could occur from
improperly connected drains or a plugged drain tube.
WARNING
HIGH VOLTAGE
Disconnect ALL power before servicing or in
-
stalling this unit. Multiple power sources may
be present. Failure to do so may cause proper
-
ty damage, personal injury or death.
1. Remove burner compartment door to gain access to
pressure switch(es).
2. Remove wires from the pressure switch(es) electrical
terminals.
3. Remove the pressure control hose from the control
and interconnect with an inclined manometer as
shown in the following figures.
4. With an ohm meter connected across the pressure
switch terminals; with the inducer running the switch
should close and the ohm meter should show a
complete circuit across the pressure switch. If the
switch is not closed, compare the negative pressure
to the closing point specified for the particular switch.
Either the switch is defective or the inducer / venting
system is inadequate.
S-311 High Altitude Application (USA)
A high altitude kit is required for installations above
7,000 ft. Refer to the accessory matrix in this manual to
determine the proper natural gas and LP gas high altitude
kit for your furnace.
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
bypass or alter furnace controls.
If delayed ignition should occur, the following should be
checked:
SERVICING
