437758-YIM-A-0409
26
Johnson Controls Unitary Products
If the low pressure switch does not close within 10 seconds of
inducer energizing, the control board 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 control board 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 control board energizes the pilot gas valve and spark outputs
for an 85 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 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.
Pilot Flame Stabilization Period
The control board de-energizes the spark output, and waits for
a 2 second flame stabilization period before energizing the
main gas valve.
If flame is lost during the flame stabilization period, the control
board counts it as a flame loss and retries ignition or locks out
flashing a “5” on the LED.
Heat Blower On Delay
The control board waits for 30 seconds and then energizes the
indoor blower heat speed. Blower on delay time begins at the
start of flame proving period in the trial for ignition.
If the thermostat demand for heat is removed, the control de-
energizes the gas valve, energizes the blower on heat speed
and initiates a post-purge and heat blower off delay.
Main Burner Operation
High Heat Warm-up
Two stage models run high heat for the first 60 seconds following
Pilot Flame Stabilization period regardless of W2 demand. If W2
is not energized at the end of this 60 second period the control de
energizes the high gas output and steps the inducer to low
speed. If W2 is energized the control remains on high heat.
There is no high heat warm-up on single stage models.
Low Heat
The control board keeps the pilot gas valve, 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 2.0
second and counts the flame loss. If flame has been lost more
than 16 times within the same call for heat, the control board
locks out flashing “5” on the LED. If flame has been lost less
than 16 times, the control attempts re-ignition after a 300
second inter-purge period.
High Heat
If the W2 terminal was energized more than 1 second before
W1 at the start of the call for heat, and remains continuously
energized through the call for heat, the control considers it to be
connected to a single stage thermostat and implements a 10
minute Auto staging feature. The 2nd stage thermostat call is
ignored until 10 minutes into steady heat (9 minutes after high
heat warm-up ended).
The control recognizes a call for 2nd stage heat when W2 is
energized (connected to “R”). The control energizes the high
gas output and induced draft motor on high speed.
If the call for 2nd stage heat goes away and the 1st stage call
remains, the control de energizes the high gas valve, drops
inducer speed to low, 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 control board runs the induced draft motor for a 30 second
post-purge period, and 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.
Heat Blower Off Delay
The control board de-energizes the indoor blower motor after a
delay time as selected by movable shunt (60, 90, 120 or 180
seconds). Blower timing begins when the thermostat is satisfied
or heat cycle was interrupted. The control returns to standby
when the blower off delay is complete.
If the thermostat call for heat returns before the blower off delay
is complete, the control begins an ignition sequence with pre-
purge while the blower off delay continues.
Lockout
While in lockout, the control board keeps the pilot gas valve,
main gas valve and induced draft motor de-energized.
