GAS HEATING SEQUENCE OF OPERATIONS
When the thermostat calls for the first stage of heating, the
When the thermostat has been satisfied, heating calls are ceased. The GV is immediately closed. The blower is de- energized after the fan off delay for heating has elapsed. The draft motor performs a
IGNITION CONTROL BOARD
FIRST STAGE OF HEATING
When the ICB receives a call for first stage of heating, “W1,” the draft motor is energized. Once the draft motor has been proven, a
During the flame stabilization period, a loss of the flame for 2 seconds will cause the main valves to close and the retry operation to begin. After the flame stabilization period, a loss of flame for 3/4 second will cause the main valves to close and the retry operation to begin.
At the conclusion of the flame stabilization period, the ICB will operate the gas heat in high fire (both valves open) for an additional 100 seconds (for a total for 120 seconds of high fire operation). After this 100 seconds, the ICB will then use the call for the second stage of heat to control the second main valve of the GV.
When “W1” is satisfied, both valves are closed.
SECOND STAGE OF HEATING
When the ICB receives a call for the second stage of heating, “W2,” the ICB conducts a complete first stage ignition sequence. If this sequence is satisfied, the second main valve of the GV is opened.
When “W2” is satisfied, the second main valve is closed.
RETRY OPERATION
When a flame is lost or is not detected during an attempt to achieve ignition, a retry operation occurs. A
If the unit fails after three ignition attempts, the furnace is
RECYCLE OPERATION
When a flame is lost after the flame stabilization period, a recycle operation occurs. If the unit fails after five recycle attempts, the furnace is
GAS HEATING OPERATION ERRORS
LOCK-OUT
A
TEMPERATURE LIMIT
If the UCB senses zero volts from the high temperature limit, the indoor blower motor is immediately energized. When the UCB again senses 24 volts from the temperature limit, the draft motor will perform a
This limit is monitored regardless of unit operation status, i.e. this limit is monitored at all time.
If the temperature limit opens three times within one hour, it will
FLAME SENSE
Flame sensing occurs at all times. If “W1” is not present and a flame is sensed for 2 seconds, the draft motor is energized and the main valve is kept off. The ICB halts any operation until a flame is not detected. Once the flame detection is lost, the ICB performs a
If “W1” is present, a flame is sensed, but the main valve is not energized, the draft motor is energized until the flame detec- tion is lost. Normal operation is now allowed.
The flame detection circuitry continually tests itself. If the ICB finds the flame detection circuitry to be faulty, the ICB will not permit an ignition sequence. Also, the draft motor is ener- gized. If this failure should occur during an ignition cycle the failure is counted as a recycle.
GAS VALVE
The UCB and ICB continuously monitor the GV.
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