403134-YIM-E-0311
Johnson Controls Unitary Products
55
4.
Cracked heat exchanger tube(s). If a heat exchanger tube or
tubes is cracked, then the flow through the heat exchanger
is restricted and the flame will either roll out of the tube inlet
or heat will build to an abnormal level in the burner area.
This can usually be determined by observing burner flame
with and without indoor blower operation. If the flame
changes when the blower is running compared to when it is
not, then visually inspect the heat exchanger tubes.
If all of the above are found to be in good condition or within the
operating ranges, then set the gas valve to the off position and
temporarily apply control voltage (~24 volts) to pin 6 of the 9 pin
ICB connector. With power applied to the unit, if the ICB LED
continues to flash a code 7, then replace the ICB and return unit
to operation (you must remove the temporary voltage to pin 6
before the gas valve is turned on). If the ICB LED flashes a
heartbeat, then replace the rollout switch, remove the
temporary voltage applied to pin 6, turn on the gas valve, restart
the furnace and verify proper operation of the furnace.
Unexpected Flame Presence
If a flame is present without a call for heat (flash code 8), then
the ICB will continue operation of the draft motor and the UCB
will call for indoor operation when either of the temperature limit
opens. If the unit is correctly wired and there is not a call for
heat, then check for control voltage to the gas valve. If control
voltage exists at the gas valve, then replace the ICB. If voltage
is not present at the gas valve, then replace the gas valve.
Gas Valve Stuck Off or On
If the pilot and/or the main valves are sensed to be off more
than 1 second when commanded to be on, the control will shut
off all outputs and enter a hard lockout (flash code 9). Likewise,
if the pilot and/or the main valves are sensed to be on more
than 1 second when commanded to be off, the control will shut
off all outputs and enter a hard lockout (flash code 9). The
control will not respond to thermostat demands during a hard
lockout. The only way to recover from a hard lockout is to
remove and reapply 24VAC power to the control.
Flame Sense Circuit Failure
If the control detects an internal hardware failure in the flame
sense circuit, it shuts off all outputs and enters a hard lockout
(flash code 10). The control will not respond to thermostat
demands during a hard lockout. The only way to recover from a
hard lockout is to remove and reapply 24VAC power to the
control. If problem persists after removal and reapplication of
24VAC power, the board may need to be replaced.
Symptomatic Troubleshooting
On calls for heating, the draft motor operates and the furnace
lights but the supply air blower motor does not energize after a
short delay (the room thermostat fan switch is in “AUTO”
position).
1.
Place the thermostat fan switch in the “ON” position. If the
supply air blower motor energizes, go to Step 10.
2.
If the supply air blower motor does not energize when the
fan switch is set to “ON,” check that line voltage is being
supplied to the contacts of the M2 contactor, and that the
contactor is pulled in. Check for loose wiring between the
contactor and the supply air blower motor.
3.
If M2 is pulled in and voltage is supplied at M2, lightly touch
the supply air blower motor housing. If it is hot, the motor
may be off on inherent protection. Cancel any thermostat
calls and set the fan switch to “AUTO”, wait for the internal
overload to reset. Test again when cool.
4.
If M2 is not pulled in, check for 24 volts at the M2 coil. If 24
volts is present at M2 but M2 is not pulled in, replace the
contactor.
5.
Failing the above, if there is line voltage supplied at M2, M2
is pulled in, and the supply air blower motor still does not
operate, replace the motor.
6.
If 24 volts is not present at M2, check that 24 volts is
present at the supply air blower motor terminal on the UCB.
If 24 volts is present at the UCB terminal, check for loose
wiring between the UCB and M2.
7.
If 24 volts is not present at the UCB supply air blower motor
terminal, check for 24 volts from the room thermostat. If 24
volts is not present from the room thermostat, check for the
following:
a. Proper operation of the room thermostat (contact
between R and G with the fan switch in the “ON”
position and in the “AUTO” position during operation
calls).
b. Proper wiring between the room thermostat and the
UCB.
c. Loose wiring from the room thermostat to the UCB.
8.
If 24 volts is present at the room thermostat but not at the
UCB, check for proper wiring between the thermostat and
the UCB, i.e. that the thermostat G terminal is connected to
the G terminal of the UCB, and for loose wiring.
9.
If the thermostat and UCB are properly wired, replace the
UCB.
10. If the blower motor runs with the fan switch in the “ON”
position but does not run shortly after the furnace has
ignited when the fan switch is in the “AUTO” position,
check the room thermostat for contact between R and G
during “W1” calls.
On calls for heating, the supply air blower operates but the draft
motor does not (the room thermostat fan switch is in the
“AUTO” position).
1.
The draft motor has inherent protection. If the motor shell is
hot to the touch, wait for the internal overload to reset.
2.
If the motor shell is cold with the room thermostat calling
for heat, check if 24 volts is present at the room thermostat
but not at the UCB, check for proper wiring between the
thermostat and the UCB, i.e. that the thermostat “W1”
terminal is connected to the “W1” terminal of the UCB, and
for loose wiring.
