Installation, Operation and Maintenance Manual : 036-1011(0806)
Page 24
Cancel any calls for cooling and wait for the internal
overload to reset. Test again when cool.
3. If the compressor contactor 4 is not pulled in, check for
24 volts at the compressor contactor coil. If 24 volt is
present and compressor contactor is not pulled in,
replace the contactor.
4. Failing the above, if voltage is supplied at the
compressor contactor 4, and it is pulled in, and the
compressor still doesn't operate, replace the
compressor.
5. If 24 volts is not present at compressor contactor 4,
check for 24 volts at the UCB terminal, C4. if 24 Volts are
present, check for loose wiring between C4 and the
compressor contactor.
6. If 24 volts is not present at the C4 terminal, check for 24
volts from the room thermostat at the UCB Y4 terminal.
If 24 volts is not present from the room thermostat, check
for the following :
•
24 volts at the thermostat Y4 terminal.
•
Proper wiring between the room thermostat and the
UCB.
•
Loose Wiring from the room is thermostat to the
UCB.
7. If 24 Volts is present at the UCB Y4 terminal, the
compressor may be out due to an open high pressure
switch, low pressure switch or freezestat. Check for 24
volts at the HPS4, LPS4 and FS4 terminals of the UCB.
If a switch has opened, there should be a voltage
potential between the UCB terminals e.g., if LPS4 has
opened, there will be 24 volts of potential between the
LPS4 terminals.
8. If 24 volts is present at the UCB Y4 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 at the thermostat or by
disconnection the thermostat wiring at the Y4 UCB
terminal. This will reset any installation, compressor lock
outs
NOTE : While the above steps will reset any lockouts,
compressor # 1, 2 & 3 will be held off for the ASCD, and the
compressor # 4 may be held off for a portion of the ASCD,
see the next step
9. If 24 volts is present at the UCB Y4 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.
10. 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.
11. If none of the above corrected the error, test the integrity
of the UCB, disconnect the C4 terminal wire and the
jumper it to the Y4 terminal, DO NOT jump the Y4 to C4
terminals. If the compressor engages, the UCB has
faulted.
12. If none of the above correct the error, replace the UCB.
On a call for cooling, the supply air blower motor and
compressor # 2 are operating but compressor # 1 is not (the
room thermostat fan switch is in the “AUTO” position).
1. Compressor # 2 is energized in place of compressor # 1
when compressor # 1 is unavailable for cooling calls.
Check the UCB for alarms indicating that compressor #
1 is locked out. Press and release the ALARMS button if
the LED is not flashing an alarm.
2. Check for line voltage at the compressor contactor 1,
and that the contactor is pulled in. Check for loose wiring
between the contactor and the compressor.
3. If compressor contactor 1 is pulled in and voltage is
supplied at the contactor 1, lightly touch the compressor
housing. If it is hot, the compressor 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 compressor contactor 1 is not pulled in, check for 24
volts at the coil. If 24 volts is present and compressor
contactor 1 is not pulled in, replace the contactor.
5. Failing the above, if voltage is supplied at compressor
contactor 1, and it is pulled in, and the compressor still
does not operate, replace the compressor.
6. If 24 volts is not present at compressor contactor, check
for 24 volts at the UCB terminal, C1. If 24 volts is
present, check for loose wiring between C1 and the
compressor contactor 1.
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 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, threshold 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
