Specifications

035-17377-000 REV A (0201)
Unitary Products Group 61
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 discon-
necting the thermostat wiring at the Y2 UCB terminal. This
will reset any compressor lock outs.
NOTE:
While the above step will reset any lock outs, compres-
sor #1 will be held off for the ASCD, and compressor #2 may
be held off for a portion of the ASCD. See the next step.
10. If 24 volts is present at the UCB Y2 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. 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.
12. If none of the above corrected the error, test the integrity of
the UGB. Disconnect the C2 terminal wire and jumper it to
the Y2 terminal. DO NOT jump the Y2 to C2 terminals. If
the compressor engages, the UCB has faulted.
13. If none of the above correct the error, replace the UCB.
On a call for cooling, the supply air blower motor and compres-
sor #2 are operating but compressor #1 is not (the room ther-
mostat 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, M1,
and that the contactor is pulled in. Check for loose wiring
between the contactor and the compressor.
3. If M1 is pulled in and voltage is supplied at M1, 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 M1 is not pulled in, check for 24 volts at the M1 coil. If
24 volts is present and M1 is not pulled in, replace the
contactor.
5. Failing 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 are not present at the UCB Y1 terminal, the UCB
may have faulted. Check for 24 volts at the Y1 ECON ter-
minal. 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 com-
pressor 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 termi-
nals.
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 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. This will reset any compres-
sor lock outs.
NOTE:
While the above step will reset any lock outs, compres-
sor #2 will be held off for the ASCD, and compressor #1 may
be held off for a portion 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 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 com-
pressor 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.