127408-YIM-B-0606
Unitary Products Group
57
11. If 24 volts is present at the UCB Y1 terminal and the
compressor is not out due to a protective switch trip,
repeat trip lock out, or ASCD, the economizer terminals
of the UCB may be improperly wired. Check for 24 volts
at the Y1 “OUT” terminal of the UCB. If 24 volts is
present, trace the wiring from Y1 “OUT” for incorrect wir-
ing. If 24 volts is not present at the Y1 “OUT” terminal,
the UCB must be replaced.
12.
For units without economizers
: If 24 volts is present at
the Y1 “OUT” terminal, check for 24 volts at the Y1
“ECON” terminal. If 24 volts is not present, check for
loose wiring from the Y1 “OUT” terminal to the Mate-N-
Lock plug, the jumper in the Mate-N-Lock plug, and in
the wiring from the Mate-N-Lock plug to the Y1 “ECON”
terminal.
For units with economizers
:If 24 volts is present at the
Y1 “OUT” terminal, check for 24 volts at the Y1 “ECON”
terminal. If 24 volts is not present, check for loose wiring
from the Y1 “OUT” terminal to the Mate-N-Lock plug, a
poor connection between the UCB and economizer
Mate-N-Lock plugs, loose wiring from the Mate-N-Lock
plug to the economizer, back to the Mate-N-Lock plug,
and from the Mate-N-Lock plug to the Y1 “ECON”
terminal. The economizer control may have faulted and
is not returning the 24 volts to the Y1 “ECON” terminal
even though the economizer is not providing free
cooling. To test the economizer control, disconnect the
Mate-N-Locks and jumper between the WHITE and
YELLOW wires of the UCB’s Mate-N-Lock plug.
13. The UCB can be programmed to lock out compressor
operation during free cooling and in low ambient condi-
tions. These options are not enabled by default. They
can be checked by local distributors.
For units with factory installed economizers, the UCB is
programmed to lock out compressor operation when the
LAS set point is reached.
For units without factory installed or with field installed
economizers, the UCB allows compressor operation all
the time. This programming can be checked or changed
by the local distributor.
14. If none of the above corrected the error, test the integrity
of the UCB. Disconnect the C1 terminal wire and jumper
it to the Y1 terminal. DO NOT jump the Y1 to C1 termi-
nals. If the compressor engages, the UCB has faulted.
15. If none of the above correct the error, replace the UCB.
GAS HEAT TROUBLESHOOTING GUIDE
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 9.
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 M3 contactor, and
that the contactor is pulled in. Check for loose wiring
between the contactor and the supply air blower motor.
3.
If M3 is pulled in and voltage is supplied at M3, 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 M3 is not pulled in, check for 24 volts at the M3 coil. If
24 volts is present at M3 but M3 is not pulled in, replace
the contactor.
5.
Failing the above, if there is line voltage supplied at M3,
M3 is pulled in, and the supply air blower motor still does
not operate, replace the motor.
6.
If 24 volts is not present at M3, 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 M3.
a.
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:
i.
Proper operation of the room thermostat (con-
tact between R and G with the fan switch in the
“ON” position and in the “AUTO” position during
operation calls)
ii.
Proper wiring between the room thermostat and
the UCB, and
iii.
Loose wiring from the room thermostat to the
UCB
7.
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 con-
nected to the G terminal of the UCB, and for loose wir-
ing.
8.
If the thermostat and UCB are properly wired, replace
the UCB.
The furnace may shut down on a high temperature
condition during the procedure. If this occurs, the
UCB energize the supply air blower motor until the
high temperature limit has reset. Caution should be
used at all times as the supply air blower may ener-
gize regardless of the room thermostat fan switch
position.
