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OAU-SVX007A-EN 95
recirculation into combustion air supply. If surrounding
buildings or prevailing winds cause recirculation, a flue
extension may be required to prevent recirculation.
Contact manufacturer prior to making any flue
adjustments.
• Reduced air delivery can also be the result of inducer
fan blade slippage, dirt accumulation in the fan blade or
low voltage to draft inducer motor. Inspect draft fan
assembly and be sure fan blade is secure to motor
shaft. Check line voltage to heater.
6. Flame Sensor Current Check
Flame current is the current which passes through the
flame from the sensor to ground. A flame signal of 0.5 to
1.0 microamp (A) is marginal. For dependable operation,
a flame signal of greater than 1.0 A is required. To
measure flame current, connect a meter capable of
reading micro-amp current so the flame signal will be read
thru the meter’s COM and A connections. The meter
should read greater than 1.0 A.
Note: If the meter reads below “0” on scale, meter leads
are reversed; disconnect power and reconnect
meter leads for proper polarity.
.
Safety Controls
Air Pressure Switch: An air pressure switch is provided
as part of the control system to verify airflow through draft
inducer by monitoring the difference in pressure between the
draft inducer and the atmosphere. If sufficient negative
pressure is not present, indicating lack of proper air movement
through heat exchanger, the switch opens shutting off gas
supply though the ignition control module. On units with two
speed draft inducer operation, a dual air pressure switch is
used, monitoring high and low speed pressures. The air
pressure switches have fixed settings and are not adjustable.
Rollout Switch (Manual Reset): The furnace module is
equipped with manual reset rollout switch(es) in the event of
burner flame rollout. The switch will open on temperature rise
and shut-off gas supply through the ignition control module.
Flame rollout can be caused by insufficient airflow for the
burner firing rate (high gas pressure), blockage of the vent
system or in the heat exchanger. The furnace module should
not be placed back in operation until the cause of rollout
condition is identified and corrected. The rollout switch can be
reset by pressing the button on top of the switch.
High Limit Switch: The furnace module is equipped with a
fixed temperature high limit switch mounted on the vestibule
panel that shuts off gas to the heater through the ignition
control module in the event of reduced airflow over the heat
exchanger tubes. Reduced airflow can be caused by indoor
fan failure, dirty or blocked filters, or restriction of the air inlet
or outlet to the unit. The high limit switch will automatically reset
when the air temperature drops to approximately 30°F below
the limit setpoint. Determine the cause of the reduced airflow
and correct.
NOTICE
Meter Damage!
Measuring voltage with meter connect to a circuit could
result in meter damage. Do NOT measure voltage with
meter connected to a circuit.
Figure 144. OAK/OAN indirect fired gas furnace components
Inducer motor
Ignition
Controllers
On/Off gas valve
On/Off gas valve
Manifold gas
pressure tap
Manifold gas
pressure tap 3.5 in. WC
Air-proving switch
Condensate drain
(TYP. 2)
Inducer blower
Modulating valve
inlet pressure tap 5 in. WC
Flame
sensor
High limit
switch
Rollout
switch
Rollout
switch
Modulating
gas valve
Minimum/maximum inlet pressure =
7 IN. WC/14 in. WC (1.7 KPA/3.5 KPA)
for natural gas and 10 in. WC/14 in. WC
(2.5 KPA/3.5 KPA) for propane
Minimum/maximum inlet pressure =
7 IN. WC/14 in. WC (1.7 KPA/3.5 KPA)
for natural gas and 10 in. WC/14 in. WC
(2.5 KPA/3.5 KPA) for propane
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