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292447-YIM-A-0507
Unitary Products Group 61
10. If 24 volts is present at the UCB Y2 terminal and none of
the switches are open and the compressor is not locked
out, the UCB may have the compressor in an ASCD.
Check the LED for an indication of an ASCD cycle. The
ASCD should time out within 5 minutes. Press and release
the TEST button to reset all ASCDs.
11. The UCB can be programmed to lock out compressor
operation during free cooling and in low ambient
conditions. These options are not enabled by default. Local
distributors can test the UCB for this programming.
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.
12. If none of the above corrected the error, test the integrity of
the UCB. Disconnect the C2 terminal wire and jumper it to
the Y2 terminal. DO NOT jump the Y2 to C2 terminals. If
the compressor engages, the UCB has faulted.
13. If none of the above correct the error, replace the UCB.
On a call for cooling, the supply air blower motor and
compressor #2 are operating but compressor #1 is not (the
room thermostat fan switch is in the “AUTO” position):
1. Compressor #2 is energized in place of compressor #1
when compressor #1 is unavailable for cooling calls. Check
the UCB for alarms indicating that compressor #1 is locked
out. Press and release the ALARMS button if the LED is
not flashing an alarm.
2. Check for line voltage at the compressor contactor, M1,
and that the contactor is pulled in. Check for loose wiring
between the contactor and the compressor.
3. If M1 is pulled in and voltage is supplied at M1, lightly touch
the compressor housing. If it is hot, the compressor may be
off on inherent protection. Cancel any calls for cooling and
wait for the internal overload to reset. Test again when cool.
4. If M1 is not pulled in, check for 24 volts at the M1 coil. If 24
volts is present and M1 is not pulled in, replace the
contactor.
5. Failing the above, if voltage is supplied at M1, M1 is pulled
in, and the compressor still does not operate, replace the
compressor.
6. If 24 volts is not present at M1, check for 24 volts at the
UCB terminal, C1. If 24 volts is present, check for loose
wiring between C1 and the compressor contactor.
7. If 24 volts is not present at the C1 terminal, check for 24
volts from the room thermostat at the UCB Y1 terminal. If
24 volts are not present at the UCB Y1 terminal, the UCB
may have faulted. Check for 24 volts at the Y1 ECON
terminal. If 24 volts is not present at Y1 “ECON”, the UCB
has faulted. The UCB should de-energize all compressors
on a loss of call for the first stage of cooling, i.e. a loss if 24
volts at the Y1 terminal.
8. If 24 volts are present at the UCB Y1 terminal, the
compressor may be out due to an open high-pressure
switch, low-pressure switch, or freezestat. Check for 24
volts at the HPS1, LPS1, and FS1 terminals of the UCB. If
a switch has opened, there should be a voltage potential
between the UCB terminals, e.g. if LPS1 has opened, there
will be a 24-volt potential between the LPS1 terminals.
9. If 24 volts is present at the UCB Y1 terminal and none of
the protection switches have opened, the UCB may have
locked out the compressor for repeat trips. The UCB
should be flashing a code. If not, press and release the
ALARMS button on the UCB. The UCB will flash the last
five alarms on the LED. If the compressor is locked out,
remove any call for cooling. This will reset any compressor
lock outs.
NOTE: While the above step will reset any lock outs,
compressor #2 will be held off for the ASCD, and
compressor #1 may be held off for a portion of the
ASCD. See the next step.
10. If 24 volts is present at the UCB Y1 terminal and none of
the switches are open and the compressor is not locked
out, the UCB may have the compressor in an ASCD.
Check the LED for an indication of an ASCD cycle. The
ASCD should time out within 5 minutes. Press and release
the TEST button to reset all ASCDs.
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 wiring. 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