104
DIAGNOSTIC ALARM CODES AND POSSIBLE CAUSES
T051, P051 (Circuit A, Compressor 1 Failure)
T052, P052 (Circuit A, Compressor 2 Failure)
T055, P055 (Circuit B, Compressor 1 Failure)
T056, P056 (Circuit B, Compressor 2 Failure)
Alert codes 051, 052, 055, and 056 are for compressors A1,
A2, B1, and B2 respectively. These alerts occur when the cur-
rent sensor (CS) does not detect compressor current during
compressor operation. When this occurs, the control turns off
the compressor and logs a strike for the respective circuit.
These alerts reset automatically.
If the current sensor board reads OFF while the compressor re-
lay has been commanded ON for a period of 4 continuous sec-
onds, an alert is generated.
Any time this alert occurs, a strike will be called out on the af-
fected compressor. If three successive strikes occur the compres-
sor will be locked out requiring a manual reset or power reset of
the circuit board. The clearing of strikes during compressor op-
eration is a combination of 3 complete cycles or 15 continuous
minutes of run time operation. So, if there are one or two strikes
on the compressor and three short cycles (ON-OFF, ON-OFF,
ON-OFF) less than 15 minutes each occur, the strikes will be re-
set to zero for the affected compressor. Also, if the compressor
turns on and runs for 15 minutes straight with no compressor
failure, the compressor’s strikes are cleared as well.
NOTE: Until the compressor is locked out, for the first two strikes,
the alert will not be broadcast to the network, nor will the alarm re-
lay be closed.
The possible causes are:
• High-pressure switch (HPS) open. The HPS is wired in se-
ries with compressor relays on the MBB. If the high-pres-
sure switch opens during compressor operation, the com-
pressor stops, and the CS no longer detects current, caus-
ing the control to activate this alert.
• Compressor internal overload protector is open. Internal
overload protectors are used in the Copeland compressors
in all units except size 60 ton units with voltages of 208/
230-v, 380-v, and 575-v.
• Compressor external overload protector (Kriwan module)
has activated. The Copeland compressors in size 60 ton
units with voltages of 208/230-v, 380-v, and 575-v use ex-
ternal overload protector modules that are mounted in the
compressor wiring junction box. Temperature sensors em-
bedded in the compressor motor windings are the inputs to
the module. The module is powered with 120 vac from the
units main control box. The module output is a normally
closed contact that is wired in series with the compressor
contactor coil. In a compressor motor overload condition,
the contact opens de-energizing the compressor contactor.
• Circuit breaker trip. The compressors are protected from
short circuit by a breaker in the control box. On the 020-050
size units there is one breaker per two compressors and on
the 060 size units there is one breaker per compressor.
• Wiring Error. A wiring error might not allow the compres-
sor to start.
To check out alerts 051, 052, 055 and 056:
1. Turn on the compressor in question using Service Test mode.
If the compressor does not start, then most likely the problem
is one of the following: HPS open, open internal protection,
circuit breaker trip, incorrect safety wiring, or incorrect com-
pressor wiring.
2. If the compressor does start, verify it is rotating in the correct
direction.
A051 (Circuit A, Compressor 1 Stuck On Failure)
A052 (Circuit A, Compressor 2 Stuck On Failure)
A055 (Circuit B, Compressor 1 Stuck On Failure)
A056 (Circuit B, Compressor 2 Stuck On Failure)
Alarm codes 051, 052, 055, and 056 are for compressors A1,
A2, B1, B2 respectively. These alarms occur when the current
sensor (CS) detects current when the compressor should be off.
When this occurs, the control turns off the compressor and logs
a strike for the respective circuit. Use the scrolling marquee to
reset the alarm.
If the current sensor board reads ON while the compressor re-
lay has been commanded OFF for a period of 4 continuous sec-
onds, an alarm is generated. These alarms are only monitored
for a period of 10 seconds after the compressor relay has been
commanded OFF. This is done to facilitate a service technician
forcing a relay to test a compressor.
In addition, if a compressor stuck failure occurs and the current
sensor board reports the compressor and the request off, certain
diagnostics will take place.
1. If any of the 4 compressors are diagnosed as stuck on and the
current sensor board is on and the request is off, the control
will request the supply fan which will automatically start
building airflow control. Condenser fans will also be com-
manded on to maintain normal head pressure.
2. Heating will be disabled while any one of the compressors
has this problem.
The possible causes are:
• welded contactor
• frozen compressor relay on MBB
To check out alarms 051, 052, 055, and 056:
1. Place the unit in Service Test mode. All compressors should
be off.
2. Verify that there is not 24 v at the contactor coil. If there is 24
v at the contactor, check relay on MBB and wiring.
3. Check for welded contactor.
4. Verify CS wiring.
5. Return to Normal mode and observe compressor operation
to verify that compressor current sensor is working and con-
denser fans are energized after compressor starts.
IMPORTANT: Prolonged operation in the wrong direction
can damage the compressor. Correct rotation can be verified
by a gage set and looking for a differential pressure rise on
start-up.
IMPORTANT: If the compressor starts, verify that the in-
door and outdoor fans are operating properly.
IMPORTANT: If the CS is always detecting current, then
verify that the compressor is on. If the compressor is on,
check the contactor and the relay on the MBB. If the com-
pressor is off and there is no current, verify CS wiring and
replace if necessary.
IMPORTANT: Return to Normal mode and observe com-
pressor operation to verify that compressor current sensor is
working and condenser fans are energized after compressor
starts.
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