Product data

Page 21
Installation, Operation & Maintenance Manual # 036-1009(0608)
volts is not present from the room thermostat, check for the
following :
24 volts at the thermostat Y1 terminal. •
Proper wiring between the room thermostat and the •
UCB, i.e. Y1 to Y1, Y2 to Y2.
Loose wiring from the room thermostat to the UCB. •
7. 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.
8. 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,
compressor # 1 may be held off for the ASCD. See the next
step.
9. 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.
10. 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 terminals. If the
compressor engages, the UCB has faulted.
11. 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” position).
NOTE : 2nd stage of cooling is available only in DMS 150.
1. 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 seconds to prevent
a power surge. If after the delay compressor # 2 does
not energize on a second stage call for cooling, check for
line voltage at the compressor contactor 2, and that the
contactor is pulled in. Check for loose wiring between the
contactor and the compressor.
2. If compressor contactor 2 is pulled in and voltage is
supplied, 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.
3. If compressor contactor 2 is not pulled in, check for 24 volts
at the compressor contactor coil. If 24 volts is present and
compressor contactor is not pulled in, replace the contactor.
4. Failing the above, if voltage is supplied at compressor
contactor 2, and it is pulled in, and the compressor still does
not operate, replace the compressor.
5. If 24 volts is not present at compressor contactor 2, check
for 24 volts at the UCB terminal, C2. If 24 volts are present,
check for loose wiring between C2 and the compressor
contactor.
6. 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 :
24 volts at the thermostat Y2 terminal. •
Proper wiring between the room thermostat and the •
UCB, i.e. Y1 to Y1, Y2 to Y2.
Loose wiring from the room thermostat to the UCB. •
7. If 24 volts is present at the UCB Y2 terminal, the compressor
may be out due to an open high pressure switch, low
ressure 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 terminals.
8. If 24 volts is present at the UCB Y2 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 disconnecting the
thermostat wiring at the Y2 UCB terminal. This will reset any
Installation, compressor lock outs.
NOTE : While the above step will reset any lock outs,
compressor # 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.
9. 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.
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 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.
* Applicable only to DMS 150