1183746-UIM-B-0215
16
Johnson Controls Unitary Products
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 (W) is removed, the control de-energizes the gas
valve, begins post purge and heat blower off delay.
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 flashing “8” 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 postpurge, and imme-
diately 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 (W) the 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 prepurge 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 (W) for more than 1 second, or by removing power
from the control for over 0.25 seconds. The control will automatically
reset lockout after 60 minutes.
Lockouts due to detected internal control faults will reset after 60 min-
utes 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 will run the indoor blower motor on heat speed, run
the inducer, de-energize the gas valve, and flash “4” on the LED. When
the high temperature switch closes, the control will restart the ignition
sequence beginning with pre-purge.
If the limit switch has been open more than 5 minutes the control will
de-energize the inducer, continue to operate the indoor blower motor on
heat speed, and flash “11” on the LED
Rollout Switch
If the limit circuit is open for more than 15 minutes, the control board will
flash “5” on the LED. The blower output will be energized during an
open rollout condition.
If the rollout switch is reset, the control shall remain locked out until
power is removed or a call for heat (W) is removed.
Rollout switch lockout shall not reset automatically.
Power Interruptions
Power interruptions of any duration shall not cause lockout or any oper-
ation 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 will enter lockout flashing “1” on
the LED. The control will energize 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 is still sensed
as energized after the inducer has been off for 10 seconds, the control
re-energizes the inducer to vent the unburned gas. The control enters a
hard lockout flashing "10" 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, closes the main gas valve and
energizes 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 will
close.
4.
Rollout Switch (RS) - This switch is located on the burner assembly.
In the event of a sustained main burner flame rollout, the control will
close the main gas valve. The is a manual reset type switch.
NOTICE
The manual reset Rollout Switch (RS) must be reset before allowing
furnace operation.
Table 14:
Ignition Control Board Flash Codes
Flash Code
Description
Normal Operation
Green Heartbeat
Standby mode
Amber Heartbeat
Call for furnace heat active
Operational Faults
Steady ON (any color) Control failure
Rapid Amber Flash
Low flame current <1.5 VDC at test pad
1 Red Flash
Flame sensed with gas valve off
2 Red Flashes
Pressure switch closed with inducer off
3 Red Flashes
Pressure switch open with inducer on
4 Red Flashes
Limit switch or rollout switch open
5 Red Flashes
Limit switch or rollout switch open >15 minutes
6 Red Flashes
Pressure switch cycle lockout
7 Red Flashes
Lockout due to failed ignition
8 Red Flashes
Lockout due to too many flame dropouts
10 Red Flashes
Gas valve fault
11 Red Flashes
Limit/Rollout switch open between 5 and 15
minutes
Wiring Related Faults
9 Red Flashes
Incorrect low voltage polarity
4 Amber Flashes
Y thermostat demand without a G
