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035-19592-001 Rev. C (0204)
6 Unitary Products Group
If the flame is not detected within 2 seconds of the gas valve opening,
the gas valve is shut off and a retry operation begins. If the flame is lost
for 2 seconds during the 10-second stabilization period, the gas valve is
shut off and a retry operation begins. During a retry operation, the vent
motor starts a 15 second inter-purge and the ignitor warm-up time is
extended to 27 seconds. If the flame is established for more than 10
seconds after ignition during a retry, the control will clear the ignition
attempt (retry) counter. If three retries occur during a call for heat, the
furnace will shut down for one hour. If at the end of the one hour shut
down there is a call for heat, the furnace will initiate a normal start cycle.
If the problem has not been corrected the furnace will again lockout
after three retries.
A momentary loss of gas supply, flame blowout, or a faulty flame probe
circuit will result in a disruption in the flame and be sensed within 1.0
seconds. The gas valve will de-energize and the control will begin a
recycle operation. A normal ignition sequence will begin after a 15 sec-
ond inter-purge. If during the five recycles the gas supply does not
return, or the fault condition is not corrected the ignition control will lock-
out for 60 minutes.
During burner operation, a momentary loss of power for 50 milliseconds
or longer will de-energize the gas valve. When the power is restored,
the gas valve will remain de-energized and the ignition sequence will
immediately restart.
Hot Surface Ignition System
FURNACE CLEANING SECTION
NOTE: The cleaning operations listed below must be performed only by
a qualified service agency.
Burner Removal/Cleaning
The main burners should be checked periodically for dirt accumulation.
If cleaning is required, follow this procedure:
1. Turn off the electrical power to the unit.
2. Turn off the gas supply at the external manual shut-off valve and
loosen the ground union joint.
3. Remove the upper access panel and remove the burner box cover.
4. Disconnect wires from flame sensor, rollout switch and HSI igniter.
Remove igniter carefully, as it is easily broken.
5. Remove the screws that hold the burner box assembly to the vest
panel and remove the assembly.
6. Remove burners from the burner assembly.
7. Burners may be cleaned by rinsing in hot water.
8. Reassemble the burners in the reverse order.
Cleaning the Heat Exchanger
1. Turn off the electrical power to the unit.
2. Turn off the gas supply at the external manual shut-off valve and
loosen the ground union joint.
3. Remove the upper access panel and remove the burner box cover.
4. Disconnect wires from flame sensor, rollout switch and HSI igniter.
Remove igniter carefully, as it is easily broken.
5. Remove the screws that hold the burner box assembly to the vest
panel and remove the assembly.
6. Remove burners from the burner assembly.
7. Remove the upper cover plate at the top of the furnace. Remove
the internal baffle.
8. The upper portion of the heat exchanger is now exposed.
9. With a long flexible wire brush, clean inside each tube at both the
top and bottom. The brush must pass around the rear heat
exchanger tubes and then vacuum loose the scale and dirt from
each tube.
10. Clean - vacuum all burners.
11. Replace all components in reverse order. Reconnect all wiring.
12. Restore electrical power and gas supply to the furnace.
13. Check furnace operation.
Cleaning the Secondary Heat Exchanger
1. Follow steps 1 - 8 under cleaning the Heat Exchanger.
2. Remove the vent piping from the vent blower housing. Disconnect
the drain lines from the vent blower housing and from the conden-
sate drain pan. Remove the vent blower housing blower and the
condensate pan. The turbulators can then be gently removed from
the secondary heat exchanger.
3. Using a stiff wire brush, remove the loose scale or soot from each
tube.
4. Vacuum the secondary heat exchanger.
5. Finish the cleaning procedure by following steps 11 thru 13 under
cleaning the Heat Exchanger.
TROUBLESHOOTING
The following visual checks should be made before troubleshooting:
1. Check to see that the power to the furnace and the ignition control
module is ON.
2. The manual shut-off 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 blinking red LED shows a fault code. 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 indicate 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.
Flash sequence codes 1 through 11 are as follows: LED will turn “on” for
one second and “off” for one second. This pattern will be repeated the
number of times equal to the code. For example, six “on” flashes equals
a number 6 fault code. All flash code sequences are broken by a 2 sec-
ond “off” period.
HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a
match or any other means). There may be a potential
shock hazard from the components of the hot surface
ignition system. The furnace can only be lit automatically
by its hot surface ignition system.
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and danger-
ous operation. Verify proper operation after servicing.