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call for cooling. This will reset any compressor lock
outs.
While the above step will reset any lock outs,
NOTE:
compressor #2 will be held off for the ASCD,
and compressor #1 may be held off for a por-
tion 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 econo-
mizer, 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.
Johnson Controls Unitary Products
13. The UCB can be programmed to lock out compres-
sor operation during free cooling and in low ambi-
ent conditions. 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 opera-
tion 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 terminals. If the compressor
engages, the UCB has faulted.
15. If none of the above correct the error, replace the
UCB.
GAS HEAT TROUBLESHOOTING GUIDE
Troubleshooting of components may require
opening the electrical control box with the
power connected to the unit. Use extreme
care when working with live circuits! Check
the unit nameplate for the correct line voltage
and set the voltmeter to the correct range
before making any connections with line termi-
nals.
For troubleshooting of optional VFD, discon-
nect all power to the drive. Be aware that high
voltages are present in the drive even after
power has been disconnected. Capacitors
within the drive must be allowed to discharge
before beginning service.
When not necessary, shut off all electric power
to the unit prior to any of the following mainte-
nance procedures so as to prevent personal
injury.
284812-YIM-D-1008
71
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Table of Contents
Troubleshooting
