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, com- pressor #1 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 wir- ing. 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
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
14.The UCB can be programmed to lock out compressor operation during free cooling and in low ambient condi- tions. 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 termi- nals. 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” posi- tion):
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, fol- lowing a short delay, compressor #1 will be energized unless it is locked out. Typically, compressor #2 is ener- gized 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 sec- onds to prevent a power surge. If after the delay com- pressor #2 does not energize on a second stage call for cooling, check for line voltage at the compressor contac- tor, 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 compres- sor 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 com- pressor may be out due to an open
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