Installation manual
1) Call for Heat - The thermostat calls for heat by energizing the “W” terminal. The
control checks to see that the limit switches are closed and the pressure switch is
open. If one of the limit switches is open, the control responds as dened in the
“Abnormal Heat Cycle, Limit Switch Operation”. If the pressure switch is closed, the
control will do four ashes on the green LED and wait indenitely for the pressure
switch to open. If the pressure switch is open, the control proceeds to prepurge.
2) Prepurge - The control energizes the venter motor and waits for the pressure
switch to close. If the pressure switch does not close within 30 seconds of the
venter motor energizing, the control will do two ashes on the green LED. The
control will leave the venter motor energized indenitely as long as the call for heat
remains and the pressure switch is open.
When the pressure switch is proven closed, the control begins the prepurge time. If
ame is present any time while in prepurge, the prepurge time is restarted. If ame
is present long enough to cause lockout, the control responds as dened 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 ame is sensed during the rst 16 seconds, the
spark is de-energized and the control proceeds to heat fan/blower on delay. If
ame has not been sensed during the rst 16 seconds, the control de-energizes
the spark output and keeps the gas valve energized for an additional one second
ame proving period. If ame is not present after the ame proving period, the
control de-energizes the gas valve and proceeds with ignition re-tries as specied
in “Abnormal Heat Cycle, Ignition Retry”. If ame 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, ame 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 satised.
7) Fan/Blower Off Delay - The fan/blower motor is de-energized after a blower off
delay of 120 seconds.:
Normal Heat Cycle Operating Sequence
Abnormal Heat Cycle
Functions
Interrupted Thermostat Call for Heat - If the thermostat demand for heat is
removed before the ame 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 ame is not established on the rst 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 ame 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 120 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 ame is not established on the third trial for ignition period, the control de-ener-
gizes the gas valve, and the venter motor remains energized for an inter-purge
10.0 Ignition System
(cont’d)
Form I-UEAS, Page 32