5188236-BIM-A-0316
Johnson Controls Unitary Products
65
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.
3.
The draft motor is a 230 volt draft motor on all models
regardless of unit supply voltage. If the ICB is flashing a
code other than the heartbeat, then troubleshoot the device
indicated by the fault code. If not, then remove power to the
unit for more than 20 seconds. If upon restoring the power
to the unit the draft motor does not start with a call for heat,
then verify that terminal “L1” of the ICB has a minimum of
120 volts to ground on 230 and 460 volt models or a
minimum of 18 volts to ground on 575 volt models. If
terminal “L1” does not have the minimum voltage, then
check the wiring between the unit control box and the ICB
on all models and on 460 volt models, the transformer in
the gas heat compartment and its wiring. If terminal “L1”
does have the minimum voltage, then check for the
minimum voltage on terminal “IND” of the ICB on single
stage models and terminal “IND HIGH” of the ICB on two
stage models. If voltage is not present at the terminal, then
verify wiring between the control box and the ICB. If all
wiring is intact, then ICB is at fault. If voltage is present at
the terminal on 230 and 460 volt models, then the draft
motor is at fault. On 575 volt models, if voltage is present at
the terminal, then check the draft motor relay (DMR on
single stage gas heat and DMR-2 on two stage gas heat)
mounted above the ICB. First verify that the relay is pulled
in by visual inspection. If not, then verify the minimum
voltage is present between terminals “A” and “B” of the
relay. If the minimum voltage is not present, then check the
wiring. If it is present, then verify that a minimum of 150
volts is present at terminals “5” and “7” of the draft motor
relay. If not present at terminal “7” of the draft motor relay,
then troubleshoot the transformer in blower section and its
wiring. If present at terminal “7” and not at terminal “5” of
the draft motor relay, then the relay is at fault. If the
minimum voltage is present at terminal 5 of the draft motor
relay, then the draft motor is at fault.
The igniter sparks at the pilot burner but the pilot does not ignite
and a gas odor is detected at the draft motor outlet.
1.
Adjust the pilot adjust screw on the gas valve as described
in “PILOT CHECKOUT” on page 57.
2.
Check the supply pressure as described in “POST START
CHECK LIST” on page 56. Make adjustments as
necessary.
3.
Check the pilot orifice and pilot burner for obstruction as
described in paragraph above. Clean as needed but the
problem should not be the gas valve.
The pilot burner ignites but the igniter continues to spark and
the main burners do not ignite.
1.
Make the same checks and adjustment as described in
“PILOT CHECKOUT” on page 57.
2.
Check the supply pressure as described in “POST START
CHECK LIST” on page 56. Make adjustments as
necessary.
3.
Make sure that the pilot burner is not bent or damaged.
4.
Make sure that the ground connections at the pilot burner,
gas valve and ignition control are intact. Check the igniter
wire for good electrical connection. If all are intact, replace
the ignition control.
