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292447-YIM-A-0507
60 Unitary Products Group
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.
13. 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. If nothing
is found, the economizer control may have faulted and is
failing to return the 24-volt “call” to the Y1 “ECON” terminal
even though the economizer is not providing free cooling.
To test, disconnect the Mate-N-Locks and jumper between
the WHITE and YELLOW wires of the UCB’s Mate-N-Lock
plug. If compressor #1 energizes, there is a fault in the
economizer wiring or the economizer control.
14. 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.
15. 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 terminals. If
the compressor engages, the UCB has faulted.
16. If none of the above correct the error, replace the UCB.
On calls for the second stage of cooling, the supply air blower
motor and compressor #1 are operating but compressor #2 is
not (the room thermostat fan switch is in the “AUTO” position):
1. If installed, check the position of the economizer blades. If
the blades are open, the economizer is providing free
cooling. If the second stage of cooling is requested,
following a short delay, compressor #1 will be energized
unless it is locked out. Typically, compressor #2 is
energized only during free cooling if the call for the second
stage of cooling persists for 20 minutes.
2. Compressor #2 will not energize simultaneously with
compressor #1 if a call for both stages of cooling is
received. The UCB delays compressor #2 by 30 seconds
to prevent a power surge. If after the delay compressor #2
does not energize on a second stage call for cooling, check
for line voltage at the compressor contactor, M2, and that
the contactor is pulled in. Check for loose wiring between
the contactor and the compressor.
3. If M2 is pulled in and voltage is supplied at M2, 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 M2 is not pulled in, check for 24 volts at the M2 coil. If 24
volts is present and M2 is not pulled in, replace the
contactor.
5. Failing the above, if voltage is supplied at M2, M2 is pulled
in, and the compressor still does not operate, replace the
compressor.
6. If 24 volts is not present at M2, check for 24 volts at the
UCB terminal, C2. If 24 volts are present, check for loose
wiring between C2 and the compressor contactor.
7. If 24 volts is not present at the C2 terminal, check for 24
volts from the room thermostat at the UCB Y2 terminal. If
24 volts is not present from the room thermostat, check for
the following:
a. 24 volts at the thermostat Y2 terminal
b. Proper wiring between the room thermostat and the
UCB, i.e. Y1 to Y1, Y2 to Y2, and
c. Loose wiring from the room thermostat to the UCB
8. If 24 volts is present at the UCB Y2 terminal, the
compressor may be out due to an open high-pressure
switch, low-pressure switch, or freezestat. Check for 24
volts at the HPS2, LPS2, and FS2 terminals of the UCB. If
a switch has opened, there should be a voltage potential
between the UCB terminals, e.g. if LPS2 has opened, there
will be 24 volts of potential between the LPS2 terminals.
9. If 24 volts is present at the UCB Y2 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 at the thermostat or by
disconnecting the thermostat wiring at the Y2 UCB
terminal. This will reset any compressor lock outs.
NOTE: While the above step will reset any lock outs,
compressor #1 will be held off for the ASCD, and
compressor #2 may be held off for a portion of the
ASCD. See the next step.