5285473-UIM-E-1217
16
Johnson Controls Unitary Products
Heat Blower On Delay
The control board waits for 30 seconds and then energizes the indoor
blower heat speed. The indoor blower heat speed is based on the
HEAT airflow selection jumper, and the low heating (W1) or the high
heating (W1+W2) input.
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
The control board keeps the main gas valve and induced draft motor
energized while continuously monitoring the call for heat, pressure
switch and flame status.
If the call for heat (W1) is removed, the control de-energizes the gas
valve and begins the post purge and heat blower off delay.
If a call for low fire heat (W1) is present and a call for high stage heat
(W2) is removed, the control is staged down to low fire heat. The control
is staged back up to high fire heat if the high stage heat (W2) call is re-
applied to the control. During normal operation if the control is operating
the unit in low stage heat, the control is switched to high fire heat any
time a call for high stage heat (W2) is applied to the control regardless
of the setting on the HI HEAT DELAY jumper.
If the pressure switch opens, the control de-energizes the gas valve
and begins pressure switch proving mode.
If flame is removed, the control de-energizes the gas valve within 2.0
seconds and counts the flame loss. If flame has been lost less than 5
times, the control attempts re-ignition after a 15 second inter-purge
period. If flame has been lost more than 5 times within the same call for
heat, the control board locks out, and flashes a sequence of “8” times
on the LED.
Post Purge
The control board runs the induced draft motor for a 15 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 and immediately
begins the next ignition sequence.
Heat Blower Off Delay
After a heating sequence, the control board de-energizes the indoor
blower motor after a delay time as selected by a movable shunt (60, 90,
120 or 180 seconds). Blower off timing begins when the thermostat is
satisfied and removes the (W1) call for heat. 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 com-
plete, the control begins an ignition sequence with pre-purge while the
blower off delay continues.
Lockout
While in lockout, the control board keeps the main gas valve and
induced draft motor de-energized.
Lockouts due to failed ignition or flame losses may be reset by remov-
ing the call for heat (W1) for more than 1 second, or by removing power
from the control for over 0.25 second. The control automatically resets
from lockout after 60 minutes.
Lockouts due to detected internal control faults reset after 60 minutes or
power interruption. Cooling operations are available during a heating
lockout.
High Temperature Limit Switch
Any time the high temperature limit switch is open less than 5 minutes,
the control board runs the indoor blower motor on high heat speed, runs
the inducer, de-energizes the gas valve, and flashes a sequence of “4”
times on the LED. When the high temperature switch closes, the control
restarts the ignition sequence beginning with pre-purge.
If the limit switch has been open more than 5 minutes the control de-
energizes the inducer, continues to operate the indoor blower motor on
heat speed, and flashes a sequence of “11” times on the LED.
Rollout Switch
If the limit circuit is open for more than 15 minutes, the control board
flashes a sequence of “5” times on the LED. The blower output ener-
gizes on high heat speed during an open rollout condition.
If the rollout switch is reset, the control remains locked out until power is
removed or a call for heat (W) is removed.
Rollout switch lockout does not reset automatically.
Power Interruptions
Power interruptions of any duration do not cause lockout or any opera-
tion requiring manual intervention.
Flame present with Gas off
If flame is sensed for longer than 4.0 seconds during a period when the
gas valve should be closed, the control enters a lockout flashing a
sequence of “1” time on the LED. The control energizes the inducer
blower while the flame is sensed.
GAS VALVE FAULT
If the main valve output is sensed to be energized for more than 1 sec-
ond when commanded to be off, the control de-energizes the induced
draft motor (if flame is not present) to attempt to open the pressure
switch to de-energize the gas valve. If the main gas valve still senses
being energized after the inducer has been off for 10 seconds, the con-
trol re-energizes the inducer to vent the unburned gas. The control
enters a hard lockout flashing a sequence of “10” times on the LED.
The only way to recover from a hard lockout is to remove and reapply
24VAC power to the control board.
Safety Controls
The control circuit includes the following safety controls:
1.
Limit Switch (LS) - This control is located inside the blower compart-
ment and protrudes into the heat exchanger compartment and is set
to open at the temperature indicated in the Temperature Controls
Table of the unit wiring diagram. It resets automatically. The limit
switch operates when a high temperature condition occurs, thus
shutting down the ignition control, closing the main gas valve and
energizing the blower.
2.
Pressure Switch (PS) - If the draft motor should fail, the pressure
switch prevents the ignition control and gas valve from being ener-
gized.
3.
Flame Sensor - The flame sensor is located on the left-most burner.
If an ignition control fails to detect a signal from the flame sensor
indicating the flame is properly ignited, then the main gas valve
closes.
4.
Rollout Switch (RS) - This switch is located on the burner assembly.
In the event of a sustained main burner flame rollout, the control
closes the main gas valve. This is a manual reset type switch.
NOTICE
The manual reset Rollout Switch (RS) must be reset before allowing
furnace operation.
