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Table 18: Indoor Blower Specifications
Size
(Tons)
HP
RPM
024
1/2
Variable
(2.0)
030
3/4
Variable
(2.5)
036
3/4
Variable
(3.0)
042
3/4
Variable
(3.5)
048
1
Variable
(4.0)
060
1
Variable
(5.0)
Operation
The unit is controlled by a conventional heating/cooling
thermostat common to this class of equipment.
Heating Sequence Of Operation
Heat
The control board begins a call for heat when W1 is energized
(connected to R). The control ignores W2 until pilot ignition has
been established.
The control checks to see if the pressure switch is open. If the
pressure switch is closed, the control board flashes "3" on the
LED and waits indefinitely for it to open. When the pressure
switch is sensed as open, the control begins pressure switch
proving period. If the call for heat is lost, the control goes back
to Standby.
Pressure Switch Proving
The control board energizes the induced draft motor (High speed
for 2 stage model) 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 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
Johnson Controls Unitary Products
Motor
Eff.
SF
Frame
0.8
1.0
48
0.8
1.0
48
0.8
1.0
48
0.8
1.0
48
0.8
1.0
48
0.8
1.0
48
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.
508258-YIM-C-0211
21
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