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Johnson Controls Unitary Products 61
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 fur-
nace 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 con-
nected to the “W1” terminal of the UCB, and for
loose wiring.
3. The draft motor is a 230 volt draft motor on all mod-
els regardless of unit supply voltage. If the ICB is
flashing a code other than the heartbeat, then trou-
bleshoot 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 mini-
mum 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 min-
imum 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 min-
imum voltage on terminal “IND” of the ICB on sin-
gle 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 con-
trol 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 ver-
ify 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 trans-
former 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 mini-
mum voltage is present at terminal 5 of the draft
motor relay, then the draft motor is at fault.
The ignitor 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 51.
2. Check the supply pressure as described in “POST
START CHECK LIST” on page 50. Make adjust-
ments as necessary.
3. Check the pilot orifice and pilot burner for obstruc-
tion as described in paragraph above. Clean as
needed but the problem should not be the gas
valve.
The pilot burner ignites but the ignitor continues to
spark and the main burners do not ignite.
1. Make the same checks and adjustment as
described in “PILOT CHECKOUT” on page 51.
2. Check the supply pressure as described in “POST
START CHECK LIST” on page 50. Make adjust-
ments as necessary.
3. Make sure that the pilot burner is not bent or dam-
aged.
4. Make sure that the ground connections at the pilot
burner, gas valve and ignition control are intact.
Check the ignitor wire for good electrical connec-
tion. If all are intact, replace the ignition control.
The pilot burner lights and the spark stops but the main
burners do not light.
1. Check electrical connections between the ignition
control and the gas valve. If intact, check for 24
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