Johnson Controls ZL Series Installation Manual page 68

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
68 Installation Manual ZL Series 7.5- 12.5 Ton 60 Hertz R-410A
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
or 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.
If flame is lost, the control de-energizes the gas
valve within 2 seconds and counts the flame loss.
If flame has been lost more than 5 times within the
same call for heat, the control locks out flashing 5
on the LED. If flame has been lost less than 5 times,
the control attempts re-ignition after a 30 second
inter-purge period.
High heat
The ICB recognizes a call for 2nd stage heat when
W2 is energized. The control energizes the high gas
output.
If the call for 2nd stage heat goes away and the 1st
stage call remains, the control de-energizes the high
gas valve and returns to low heat operation.
Response to loss of W1, low pressure switch, and
flame are identical to low heat operation.
Post purge
The ICB runs the induced draft motor for a 5 second
post-purge period, then de-energizes the inducer. If
a call for heat occurs during post-purge, the control
finishes the post-purge, drops inducer out to re-
prove open pressure switch before continuing with
the heat cycle.
Johnson Controls Ducted Systems