5052617-UIM-E-1116
Johnson Controls Unitary Products
35
LIMIT CONTROLS
There is a high temperature limit control located on the furnace vesti-
bule panel near the gas valve. This is an automatic reset control that
provides over temperature protection due to reduced airflow. This may
be caused by:
1. A dirty filter.
2.
If the indoor fan motor should fail.
3.
Too many supply or return registers closed or blocked off.
4.
Improperly sized duct system.
The control module will lockout if the limit trips 5 consecutive times. If
this occurs, control will reset & try ignition again after 1 hour.
SECTION XI: NORMAL OPERATION AND
DIAGNOSTICS
NORMAL OPERATION SEQUENCE
The following describes the sequence of operation of the furnace. Refer
to Owners Manual for component location.
Continuous Blower
Cooling/heating thermostats have a fan switch that has an ON and
AUTO position. In the ON position the thermostat circuit is completed
between terminals R and G. The motor will operate continuously on the
speed tap that is selected through dipswitches on the furnace control
board. To obtain a different constant air circulation change dipswitches
to assign another speed tap.
Intermittent Blower - Cooling
Cooling/heating thermostats have a fan switch that has an ON and
AUTO position. In the AUTO position the thermostat circuit is completed
between terminals R and G when there is a call for cooling. The motor
will operate on the speed tap wire that is connected to the HI COOL or
LO COOL cooling terminal on the control board depending on 24V ther-
mostat input on Y1 or Y/Y2. The fan off setting is fixed at 60 seconds to
improve cooling efficiency.
Heating Cycle
When the thermostat switch is set on HEAT and the fan is set on AUTO,
and there is a call for heat, a circuit is completed between terminals R
and W of the thermostat. When the proper amount of combustion air is
being provided, the pressure switch will close, the ignition control pro-
vides a 17-second ignitor warm-up period, the gas valve then opens,
the gas starts to flow, ignition occurs and the flame sensor begins its
sensing function. The furnace fires on high fire for 10 seconds, then it
switches to low fire unless there is a heating call present on W2. The
blower motor energizes 30 seconds after the gas valve opens if a flame
is detected. Normal furnace operation continues until the thermostat cir-
cuit between R and W is opened, which causes the ignition system and
gas valve to de-energize and the burner flames to be extinguished. The
vent motor operates for 15 seconds, and the blower motor operates for
the amount of time set by the fan-off delay dip switches located on the
control board. See Figure 40. The heating cycle is now complete and
ready for the start of the next heating cycle.
If the flame is not detected within 7 seconds of the gas valve opening,
the gas valve is shut off and a retry operation begins. During a retry
operation, the vent motor starts a 15 second inter-purge and the ignitor
warm-up time is extended to 27 seconds. If the flame is established for
more than 10 seconds after ignition during a retry, the control will clear
the ignition attempt (retry) counter. If three retries occur during a call for
heat, the furnace will shut down for one hour. If at the end of the one
hour shut down there is a call for heat, the furnace will initiate a normal
start cycle. If the problem has not been corrected the furnace will again
lockout after three retries.
A momentary loss of gas supply, flame blowout, or a faulty flame probe
circuit will result in a disruption in the flame and be sensed within 1.0
seconds. The gas valve will de-energize and the control will begin a
recycle operation. A normal ignition sequence will begin after a 15 sec-
ond inter-purge. If during the five recycles the gas supply does not
return, or the fault condition is not corrected the ignition control will lock-
out for 60 minutes.
During burner operation, a momentary loss of power for 50 milliseconds
or longer will de-energize the gas valve. When the power is restored,
the gas valve will remain de-energized and the ignition sequence will
immediately restart.
TROUBLESHOOTING
The following visual checks should be made before troubleshooting:
1.
Check to see that the power to the furnace and the ignition control
module is ON.
2.
The manual shut-off valves in the gas line to the furnace must be
open.
3.
Make sure all wiring connections are secure.
4.
Review the sequence of operation. Start the system by setting the
thermostat above the room temperature. Observe the system’s
response. Then use the troubleshooting section in this manual to
check the system’s operation.
FURNACE CONTROL DIAGNOSTICS
The furnace has built-in, self-diagnostic capability. A blinking LED light
on the control board can flash red, green or amber to indicate various
conditions. The control continuously monitors its own operation and the
operation of the system. If a failure occurs, the LED light will indicate
the failure code.
The SLOW flash speed is two seconds on and two seconds off.
The other flash codes listed below have the following timing: LED light
will turn on for 1/3 second and off for 1/3 second. This pattern will be
repeated the number of times equal to the code. There will be a two-
second pause between codes. For example, the six red flash code will
flash the LED light on and off six times, then will be off for two seconds.
This pattern will repeat as long as the fault condition remains.
SLOW GREEN FLASH:
Normal operation, no thermostat calls.
SLOW AMBER FLASH:
Normal operation with call for heat.
LED STEADY OFF
– If the LED light does not flash at all, check for
power to the board and check for a blown fuse on the board. If the
board is properly powered and the fuse is not blown, the control board
may need to be replaced.
STEADY ON ANY COLOR:
Possible control failure. Remove and
check the control voltage fuse. An open fuse will result in a steady on
red LED. Turn power to the furnace off and back on. If the fault code
returns, the control board must be replaced. The control board is not
field-repairable.
CONTINUOUS AMBER FLASH:
Flame sense current is below 0.35
mirco amps. Check and clean flame sensor. Check for proper gas flow.
Verify that current is greater than 0.35 micro amps at the flame current
test pad.
1 RED FLASH:
This indicates that flame was sensed when there was
not a call for heat. The control will turn on both the inducer motor and
supply air blower. Check for a leaking or slow-closing gas valve.
2 RED FLASHES:
This indicates that the pressure switch is closed
when it should be open. The control confirms that the pressure switch
contacts are open at the beginning of each heat cycle and will not let
the ignition sequence continue if the pressure switch contacts are
closed when they should be open. Check for a faulty pressure switch or
miswiring.
3 RED FLASHES:
This indicates the pressure switch contacts are open
when they should be closed. Check for faulty inducer, blocked vent
pipe, broken pressure switch hose, disconnected pressure switch or
inducer wires or faulty pressure switch.
Never bypass any safety control to allow furnace operation. To
do so will allow furnace to operate under potentially hazardous
conditions.
Do not try to repair controls. Replace defective controls with
UPG Source 1 Parts.
Never adjust pressure switch to allow furnace operation.
