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 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” termi- nal. If nothing is found, the economizer DME may have faulted and is failing to return the 24-volt “call” to the Y1 “ECON” terminal even though the economizer is not pro- viding 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 ener- gizes, there is a fault in the economizer wiring or DME.
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 York distributors can test the UCB for this programming.
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
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 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 ter- minals.
9.If 24 volts is present at the UCB Y2 terminal and none of the protection switches have opened, the UCB may have
