035-14527-000 REV A (599)
Form 650.77-N3U
26
Unitary Products Group
around the rear heat exchanger tubes. Vacuum loose
scale and dirt from each tube.
7.
Clean - Replace all components in reverse order. Regas-
ket all surfaces which required a gasket. Reconnect all
wiring. Reattach vent pipe and gas supply lines before
restoring service to furnace. Restore electrical power,
check gas supply piping for leaks, then verify furnace
operation.
TROUBLESHOOTING
The following visual checks should be made before trouble-
shooting:
1.
Check to see that the power to the furnace and the igni-
tion control module is ON.
2.
The manual shutoff valves in the gas line to the furnace
must be open.
3.
Make sure all wiring connections are secure.
4.
Review the sequence of operation.
Start the system by setting the thermostat above the room
temperature. Observe the system's response. Then use the
troubleshooting section in this manual to check the system's
operation.
FURNACE CONTROL DIAGNOSTICS
The furnace has built-in, self diagnostic capability. If a system
problem occurs, a fault code is shown by a blinking LED. It is
located behind a clear view port in the blower compartment
door. DO NOT remove the furnace blower compartment
panel OR turn off furnace power as either action will clear the
control's memory of the fault.
The control continuously monitors its own operation and the
operation of the system. If a failure occurs, the LED will indi-
cate the failure code. If the failure is internal to the control, the
light will stay on continuously. In this case, the entire control
should be replaced as the control is not field repairable.
If the sensed failure is in the system (external to the control),
the LED will flash in the following flash-pause sequences to
indicate failure status.
Flash sequence codes 1 thru 4 are as follows. LED will turn
on for 1/4 second and off for 1/4 second. This pattern will be
repeated the number of times equal to the code. For exam-
ple, six on flashes equals a number 6 fault code.
All flash code sequences are broken by a 2 second off period.
CONTINUOUS FLASHING (1 sec on - 1 sec off):
This indi-
cates that flame was sensed when there was not a call for
heat. With this fault code the control will also turn on both the
inducer motor and supply air blower. This fault would typically
be caused by a gas valve that leaks through or is slow clos-
ing.
1 FLASH:
This fault code indicates that flame could not be
established. This no-light condition occurred 3 times during
the call for heat before locking out. This may be caused by
low gas pressure, faulty gas valve, faulty hot surface ignitor
or burner problem.
2 FLASH:
This indicates that the normally open pressure
switch contacts are stuck in the closed position. The control
confirms these contacts are open at the beginning of each
heat cycle. This would indicate a faulty pressure switch or
mis-wiring.
3 FLASH:
This indicates the normally open pressure switch
contact did not close at the beginning of the heat cycle. This
could be caused by a number of problems; faulty inducer,
blocked vent pipe, broken pressure switch hose or faulty
pressure switch.
4 FLASH:
This indicates that a primary limit, or auxiliary limit,
or rollout limit switch has opened its normally closed contacts.
With this fault code the control will operate the supply air
blower and inducer. This condition may be caused by: dirty fil-
ter, improperly sized duct system, incorrect blower speed set-
ting, incorrect firing rate or faulty blower motor. The rollout
control is manually reset. If it has opened, check for proper
combustion air, proper inducer operation, primary heat
50A51-242 IGNITION CONTROL (P/N 031-01290-000)
Normal flame sense current is approximately
2.4 microamps DC (
υ
a)
Low flame signal control lockout point is
0.15 microamps DC (
υ
a)
POWER SUPPLY POLARITY - 50A51-242 Control
Only
If the power supply polarity is reversed, the fol-
lowing unit operation will occur. On a call for heat, the
inducer will run, the HSI will glow and the gas valve will
energize and the burners will ignite. The burners will
immediately extinguish and the unit will recycle. This will
occur 3 times and then the unit will lockout. A “7” flash
code will be displayed. This code means the flame could
not be established. This occurs because the control can-
not sense flame with the power supply polarity reversed.
