Lennox OHR23-105 - Page 19

Page 19
Troubleshooting: Fan board operating sequence
Action System Response
Continuous circulating fan is connected.
(Optional connectors are available for
separate circulating fan speed tap.)
Circulating fan is energized at low speed when there is no call for heat,
cool or fan.
If fan operation is required by a call for heat, cool, or fan, the ST9103A
switches off the continuous fan speed tap before energizing the other fan
speed.
Electronic air cleaner is connected.
(Optional connectors are available for
120 Vac electronic air cleaner.)
Electronic air cleaner (EAC) connections are energized when the heat or
cool speed of the circulating fan is energized. EAC connections are not
energized when the optional continuous fan terminal is energized.
Humidity control is connected.
(Optional connectors are available for
120 Vac humidifier.)
Humidifier connections are energized when the burner motor is energized.
Troubleshooting: Burner fails to start.
Source Procedure Causes Correction
Thermostat Check thermostat settings. Thermostat in OFF or COOL Switch to HEAT.
Thermostat is set too low Turn thermostat to higher
temperature.
Safety
Overloads
Check burner motor, primary
safety control & auxiliary limit
Burner motor overload tripped Push reset button pump motor.
Overloads safety control, & auxiliary limit
switch.
Primary control tripped on safety Reset primary control.
switch
.
Auxiliary limit switch tripped on
safety
Reset auxiliary limit.
Power Check furnace disconnect
switch & main disconnect
Open switch Close switch.
switch & main disconnect.
Blown fuse or tripped circuit
breaker
Replace fuse or reset circuit
breaker.
Thermostat Touch jumper wire across
thermostat terminals on
Broken or loose thermostat wires Repair or replace wires.
thermostat terminals on
primary control. If burner
starts, then fault is in the
Loose thermostat screw
connection
Tighten connection.
starts
,
then
fault
is
in
the
thermostat circuit.
Dirty thermostat contacts Clean contacts.
Thermostat not level Level thermostat.
Faulty thermostat Replace thermostat.
CAD Cell Disconnect the flame detector
wires at the primary control If
Flame detector leads are shorted Separate leads.
wires at the primary control. If
the burner starts
,
fault is in the
Flame detector exposed to light Seal off false source of light.
the
burner
starts
,
fault
is
in
the
detector circuit.
short circuit in the flame detector Replace detector.
Primary
Control
Place trouble light probes
between the black and white
ldNlihtidit tht
Primary or auxiliary control
switch is open
Check adjustment. Set the
maximum setting.
leads. No light indicates that
no power is going to the
control.
p
Jumper terminals; if burner
starts, switch is faulty, replace
control.
Open circuit between disconnect
switch and limit control
Trace wiring and repair or replace
it.
Low line voltage or power failure Call the power company.
Place trouble light probes
between the orange and white
leads. No light indicates faulty
control.
Defective internal control circuit Replace the control.
table continued on next page