368262-UIM-B-1008
SECTION IX: NORMAL OPERATION AND DIAGNOSTICS
NORMAL OPERATION SEQUENCE
The furnace control calculates the optimum firing rate each time the wall thermostat R and W contacts close or open (at the beginning and at the end of each call for heat) based on information from the thermo- stat and past demand. UNLIKE CONVENTIONAL SYSTEMS, THE WALL THERMOSTAT DOES NOT SIMPLY TURN THE FURNACE ON AND OFF. THE FURNACE CONTROL CALCULATES THE DEMAND AND MAY CONTINUE TO FIRE THE FURNACE DURING PORTIONS OF THE THERMOSTAT "OFF" CYCLE.
When the wall thermostat R and W contacts close, indicating a call for heat, the following sequence occurs:
1.The inducer is energized and ramps up its speed until airflow is proven by the pressure switch and by the pressure sensor on the control board.
2.The hot surface ignitor is energized.
3.After a
4.When the control senses that flame is present, the circulating blower starts at low speed.
5.The furnace fires at 70% of full rate for
6.The firing rate is automatically adjusted to meet demand, increas- ing gradually to maximum (100%) firing rate if the thermostat is not satisfied within a defined time.
7.When the thermostat R and W contacts open (thermostat is satis- fied) the furnace control recalculates the demand and a new firing rate.
a.If demand exceeds the minimum firing rate, the burners will continue to fire at a recalculated reduced firing rate, decreas- ing if the thermostat remains off for a defined time.
b.If demand does not exceed the minimum firing rate, the burn- ers will shut off immediately.
8.After the burners shut off, the circulating blower will continue to run until the temperature sensor detects that the supply air tempera- ture has dropped to the desired level, which should take from 30 to 90 seconds.
FURNACE CONTROL DIAGNOSTICS
This furnace has
STEADY OFF - No 24V power to board. Check the 24 volt control cir- cuit fuse on the board. Check the circuit breaker or fuse on the 115 volt supply power to the furnace. Check that the 24 volt transformer.
One Green Flash - Normal Operation with no call for heat.
Two Green Flashes - Indicator for "No error codes in memory". See Diagnostic Fault Code Storage and Retrieval section below.
Three Green Flashes - Indicator for "Error codes cleared from mem- ory". See Diagnostic Fault Code Storage and Retrieval section below.
Rapid Green Flash - Control is in "Factory
One Amber Flash - Normal operation with call for cooling. Two Amber Flashes - Normal operation with call for heat.
Three Amber flashes - Normal operation, burner is on at end of heat- ing cycle after wall thermostat has been satisfied.
Four Amber Flashes - Heating capacity is reduced due to restriction in the circulating air system. Check for dirty filter or closed registers.
Five Amber Flashes - Heating capacity is reduced due to restriction in the combustion air or vent system. Check for blocked vent/air pipe or clogged condensate drain. Above 4,000 feet altitude, this may also indi- cate automatic, normal derating for altitude. See page 7 for additional high altitude information.
Six Amber Flashes - (Heat Pump applications only) Normal operation with call for heat pump heating.
Rapid Amber Flash - Low flame sense current. Check for dirty or mis- located flame sensor rod.
One Red Flash - Flame is present with no power being supplied to gas valve. This can be caused by a gas valve that is slow to close or that leaks gas through to the burners.
Two Red Flashes - Pressure switch closed with inducer pressure below pressure switch setpoint (switch is closed when it should be open). Check pressure switch.
Three Red Flashes - Pressure switch open with inducer pressure above pressure switch setpoint (switch is open when it should be closed). Check pressure switch.
Four Red Flashes - High limit switch open or defective temperature sensor or 24 volt fuse is open. This may be caused by a dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow an open fuse on the control board.
Five Red Flashes - Rollout switch or condensate pressure switch open. Check the rollout switch(es) on the burner assembly. It is a man- ual reset switch. To reset, push the small button in the center of the switch. If it cannot be reset or if the switch trips again, contact a quali- fied serviceman.
Six Red Flashes - Current failure on modulating gas valve.
Seven Red Flashes - Lockout due to no ignition. The control will try three times for ignition. If flame cannot be established in three tries, the control will lockout for one hour and then will try again to light. Check gas supply, ignitor, gas valve, flame sensor.
Eight Red Flashes - Lockout due to too many flame recycles. This flash code occurs if flame is lost five times during a single heating cycle. This could be caused by a faulty gas valve, low gas pressure, or dirty flame sensor. The control will lock out for one hour and then will try again.
Nine Red Flashes - Reversed line polarity or improper grounding. Check polarity of the incoming power to the furnace. Check the ground- ing of the furnace, including the transformer ground and the L1 and neutral connections.
Ten Red Flashes - Gas valve circuit shorted. Check gas valve wiring. If correct, replace gas valve.
Eleven Red Flashes - Main blower failure - This flash code occurs when the main limit opens and fails to reclose within five minutes, indi- cating that the blower motor or blower wheel has failed.
Twelve Red Flashes - ID plug is not present or not connected properly, check for loose plug or loose wires in plug.
Steady On Red - Control fault has been detected or there is 24 volts present without 115 volts. Check that there is 24 volts and 115 volts being supplied to the board. If so, then the board should be replaced.
IGNITION CONTROL FLAME SENSE LEVELS Normal flame sense current is approximately 3.7 microamps DC (µa)
Low flame signal warning starts at 1.5 microamps.
Low flame signal control lockout point is
0.1 microamps DC (µa)
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