5742639-JIM-C-0220
Johnson Controls Ducted Systems 59
4. If M1 is not pulled in, check for 24 volts at the M1 coil. If 24
volts are present and M1 is not pulled in, replace the
contactor.
5. Following 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 is not present from the room thermostat, check for
the following:
a. 24 volts at the thermostat Y1 terminal
b. Proper wiring between the room thermostat and the
UCB, i.e. Y1 to Y1, Y2 to Y2
c. Loose wiring from the room thermostat to the UCB.
8. If 24 volts is 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 an alarm 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, cancel any call for cooling. This will reset any
compressor lock outs.
NOTE: While the above step will reset any lockouts, the
compressor may be held off for 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.
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 actuator 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 the compressor energizes, there is a fault in the
economizer wiring or actuator.
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 correct the error, replace the UCB.
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