Johnson Controls ZY Series, Installation Manual

Page: 119 / 144

Gas Heat Ignition Control
Board Function
Ignition Control Board on
Standby
The Ignition Control Board (ICB) has all outputs de-
energized and monitors the thermostat and flame
sense. The ICB resets ignition trial and flame loss
counters. The ICB begins a call for heat when W1 is
energized at the Unit Control Board (UCB). The ICB
ignores W2 until ignition has been established.
Call for heat
The ICB checks to see if the pressure switch is open.
If the pressure switch is closed, the ICB flashes "3"
on the LED and waits indefinitely for it to open.
When the pressure switch is sensed as open, the ICB
begins pressure switch proving period. If the call for
heat is lost, the ICB goes back to Standby.
Pressure switch proving
The ICB energizes the induced draft motor and
waits for the low pressure switch to close. When the
low pressure switch closes, the control begins Pre-
purge period. If the call for heat is lost, the control
de-energizes the inducer without post-purge and
returns to standby.
If the low pressure switch does not close within 10
seconds of inducer energizing, the control flashes
"2" on the LED. If the pressure switch does not close
within 5 minutes of inducer energizing, the control
shuts off the inducer for 30 seconds, then energizes
the inducer for another 5 minute try to close the
pressure switch. This cycle continues indefinitely
until either the pressure switch is proved closed, or
the call for heat ends.
Pre-purge
The ICB monitors the low pressure switch and
ensures it remains closed during pre-purge. If the
pressure switch opens, the control goes back to
pressure switch proving mode. The control waits
for a 15 second pre-purge period, then begins the
ignition trial.
Ignition trial period
The ICB energizes the main gas valve, second stage
gas valve and spark outputs for a 10 second Ignition
trial. The control de-energizes the spark when flame
is sensed and enters a flame stabilization period.
If flame is not established within the ignition trial
period, the control de-energizes the spark and gas
valve and checks for maximum number of ignition
trials. The ICB has a maximum number of 3 ignition
trials. If the control has attempted the maximum
number of ignition trials within the same call for
heat without flame, the control will lockout flashing
"4" on the LED. If the control has attempted less
than maximum ignition trials, it begins an inter-
purge period before attempting another ignition
trial.
If the call for heat is lost during an ignition trial
period, the control immediately de-energizes
spark and gas. The control runs the inducer motor
through a post purge period before de-energizing.
If the pressure switch is lost during an ignition trial
period, the control immediately de-energizes spark
and gas. The control begins pressure switch proving
before an inter-purge and re-ignition attempt.
Flame stabilization period
If a flame is detected during the Ignition Trial
Period, the ICB then enters the flame stabilization
period. If a flame is not detected in 2 seconds, the
main valve is de-energized and a retry operation
begins. The flame stabilization period lasts 10
seconds. flame detection must be lost for 2 seconds
during flame stabilization for the main valve to be
de-energized. When the flame stabilization period
has ended, a loss of flame detection for 3/4 seconds
will result in the main valve being de-energized.
If flame is lost during the flame stabilization period,
the control counts it as a flame loss and retries
ignition or locks out as described in Low heat
section.
Main Burner operation
High heat warm-up
Two stage models run high heat for the first
30 seconds following flame stabilization period
regardless of W2 demand. If W2 is not energized
at the end of this 30 second period the control de-
energizes the high gas output. If W2 is energized
the control remains on high heat.
Low heat
The ICB keeps the main gas valve and induced draft
motor energized while continuously monitoring the
call for heat, low pressure switch, and flame status.
If the call for heat (W1) is lost, the control de-
energizes the gas valve and begins post purge.
If low pressure switch opens, the control de-
energizes the gas valve and begins pressure switch
proving mode.
INSTALLATION MANUAL ZY SERIES 3 - 10 ton 60 Hertz R-410A 119
Johnson Controls Ducted Systems