66396-YIM-C-1004
Unitary Products Group
35
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-pres-
sure 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 ter-
minals, 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,
compressors #3 and #4 will be held off for the
ASCD, and compressors #1 and #2 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 compres-
sor 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 econ-
omizer 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 conditions. These options are not
enabled by default. They can be checked by local
distributors.
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 terminals. If the compressor
engages, the UCB has faulted.
15. If none of the above correct the error, replace the
UCB.
UNIT FLASH CODES
Various flash codes are utilized by the unit control
board (UCB) to aid in troubleshooting. Flash codes are
distinguished by the short on and off cycle used
(approximately 200ms on and 200ms off). To show
normal operation, the control board flashes a 1 second
on, 1 second off "heartbeat" during normal operation.
This is to verify that the UCB is functioning correctly.
Do not confuse this with an error flash code. To prevent
confusion, a 1-flash, flash code is not used.
Current alarms are flashed on the UCB LED. Pressing
and releasing the ALARMS button on the UCB can
check the alarm history. The UCB will cycle through the
last five (5) alarms, most recent to oldest, separating
each alarm flash code by approximately 2 seconds.
In some cases, it may be necessary to "zero" the
ASCD for the compressors in order to perform trouble-
shooting. To reset all ASCDs for one cycle, press and
release the UCB TEST button once.
