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Form RZ-NA I-UDA, P/N 195673 Rev 5, Page 20
20. Ignition
System
(cont’d)
Abnormal Heat
Cycle Functions
Normal Heat
Cycle Operating
Sequence (cont’d)
When the pressure switch is proven closed, the control begins the prepurge time.
If flame is present any time while in prepurge, the prepurge time is restarted. If
flame is present long enough to cause lockout, the control responds as defined in
“Fault Modes, Undesired Flame”.
The control runs the venter motor for a 20 second prepurge time, then proceeds to
the ignition trial period.
3) Ignition Trial Period - The control energizes the spark and main gas valve.
The venter remains energized. If flame is sensed during the first 16 seconds, the
spark is de-energized and the control proceeds to heat fan/blower on delay. If
flame has not been sensed during the first 16 seconds, the control de-energizes the
spark output and keeps the gas valve energized for an additional one second flame
proving period. If flame is not present after the flame proving period, the control
de-energizes the gas valve and proceeds with ignition re-tries as specified in “Ab-
normal Heat Cycle, Ignition Re-try”. If flame is present, the control proceeds to
the fan/blower on delay.
4) Fan/Blower On Delay - The control waits for 30 seconds from the time the gas
valve opened and then energizes the fan/blower motor. The gas valve and venter
motor remain energized. The control proceeds to steady heat mode.
5) Steady Heat - Control inputs are continuously monitored to ensure limit and
pressure switches are closed, flame is established, and the thermostat call for heat
remains. When the thermostat call for heat is removed, the control de-energizes
the gas valve and begins post-purge and fan/blower off delay timing.
6) Post Purge - The venter motor output remains on for a 45 second post-purge
period after the thermostat is satisfied.
7) Fan/Blower Off Delay - The fan/blower motor is de-energized after a blower
off delay as selected by the dip switches. Timing begins when the thermostat is
satisfied. Delay times are as follows:
SW1 SW2 Time
OFF OFF 120 seconds (default when shipped)
OFF ON 90 seconds
ON OFF 160 seconds
ON ON 180 seconds
Interrupted Thermostat Call for Heat - If the thermostat demand for heat is
removed before the flame is recognized, the control will run the venter motor for
the post purge period and de-energize all outputs.
If the thermostat demand for heat is removed after successful ignition, the control
will de-energize the gas valve, run the venter motor through post purge, and run
the fan/blower motor on heat speed for the selected delay off time.
Ignition Retry - If flame is not established on the first trial for ignition period, the
control de-energizes the gas valve and the venter motor remains energized for an
inter-purge period of 10 seconds. The spark and gas valve are then re-energized,
and the control initiates another trial for ignition.
If flame is not established on the second trial for ignition, the control de-energizes
the gas valve, energizes the fan/blower motor on heat speed, and venter motor
remains energized. The fan/blower motor is shut off after the longest selectable
fan delay time (180 seconds). When the fan/blower motor de-energizes, the spark
and gas valve are re-energized and the control initiates another trial for ignition.
(This fan delay is self-healing feature for an open auxiliary limit switch).
If flame is not established on the third trial for ignition period, the control de-
energizes the gas valve, and the venter motor remains energized for an inter-purge
period of 10 seconds. The control then re-energizes the gas valve and spark and
initiates another trial for ignition.