Carrier 48AJ Operating And Service Manual page 89

• Compressor internal overload protection is open. The inter-
nal overloads are used on the Scroll Tech compressors
(black) and smaller Maneurop compressors used on the 020,
025, 027, 030, 035 units and 040 A1, A2 compressors.
• Internal compressor temperature sensor trip. The large
Maneurop compressors (blue) used on the 040 B1, B2, 050,
and 060 units have an internal temperature sensor.
• Circuit breaker trip. The compressors are protected from
short circuit by a breaker in the control box. On the 020-035
and 040 A1, A2 units there is one breaker per two compres-
sors and on the 040 B1, B2 and 050, 060 compressors there
is one breaker per compressor because there is not internal
overloads.
• Wiring error. A wiring error might not allow the compressor
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 compressor wiring.
2. If the compressor does start verify it is rotating in the
correct direction.
IMPORTANT: Prolonged operation in the wrong direction
can damage the compressor. Correct rotation can be veri-
fied by a gage set and looking for a differential pressure
rise on start-up.
IMPORTANT: If the compressor starts, verify that the
indoor 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 compres-
sor starts.
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
alert.
If the current sensor board reads ON while the compressor
relay has been commanded OFF for a period of 4 continuous
seconds, an alarm is generated. These alarms are only moni-
tored for a period of 10 seconds after the compressor relay has
been commanded OFF. This is done to facilitate a service tech-
nician forcing a relay to test a compressor.
In addition, if a compressor stuck failure occurs and the cur-
rent 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 automati-
cally start building air flow control.
2. Heating will be disabled while any one of the compres-
sors 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 24v at the contactor coil. If there is
24v 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 opera-
tion to verify that compressor current sensor is working
and condenser fans are energized after compressor starts.
T064 (Circuit A Saturated Condensing Thermistor Failure)
T065 (Circuit B Saturated Condensing Thermistor Failure) —
Alert codes 064, and 065 are for circuits A and B, respectively.
These alerts occur when the saturated condensing temperatures
→
(Temperatures REF.T
range –40 to 240 F (–40 to 116 C). When this occurs, the con-
trol uses the outdoor temperature (OAT) to control the outdoor
fans. The control will default to control based on the OAT
sensor and will turn on OFC.B when the ambient is above 65 F
and off when the ambient is below 50 F.
If the SCT and OAT sensors have all failed then the control
should turn on OFC.B when compressors are on.
The cause of the alert is usually a faulty thermistor, a
shorted or open thermistor caused by a wiring error, or a loose
connection.
T072 (Evaporator Discharge Reset Sensor Failure) — If the
unit is configured to use the remote EDT 4 to 20 mA reset in-
→
put (Configuration EDT.R
is less than 2 mA then the alert will occur. When this occurs the
control will default to the internal set points. The sensor is
connected to the optional CEM module. For this sensor to be
used, the EDT 4 to 20 mA reset input (Configuration
→ →
EDT.R RES.S) must be set to "enabled."
T073 (Outside Air Temperature Thermistor Failure) — This
alert occurs when the outside air temperature sensor (Temper-
→ →
atures AIR.T OAT) is outside the range –40 to 240 F
(–40 to 116 C). Failure of this thermistor (Tempera-
→ →
tures AIR.T OAT) will disable any elements of the control
which requires its use. Economizer control beyond the vent
position and the calculation of mixed air temperature for the
sumZ algorithm will not be possible. This alert resets automati-
cally. The cause of the alert is usually a faulty thermistor, a
shorted or open thermistor caused by a wiring error, or a loose
connection.
T074 (Space Temperature Thermistor Failure) — This alert
occurs when the space temperature sensor (Temperatures
→ →
AIR.T SPT) is outside the range –40 to 240 F (–40 to
116 C). This alert will only occur if the unit is configured to use
a space temperature sensor. Configuration is done through
the Unit Control Type (Configuration
configuration. Failure
→ →
tures AIR.T SPT) will disable any elements of the control
which requires its use. If the unit is configured for SPT 2 stage
or SPT multi-stage operation and the sensor fails, no cooling or
heating mode may be chosen. This alert resets automatically.
The cause of the alert is usually a faulty thermistor in the T55,
T56, or T58 device, a shorted or open thermistor caused by a
wiring error, or a loose connection.
89
→
SCT.A and SCT.B) are outside the
→
RES.S) and the sensor reading
→ →
UNIT
of this thermistor (Tempera-
C.TYP)