Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 125

DIAGNOSTIC ALARM CODES AND POSSIBLE CAUSES
T048 (Ckt A, Oil Return Not Reliable with Only One Comp
Available)
T049 (Ckt B, Oil Return Not Reliable with Only One Comp
Available)
Alert codes T048 and T049 are for Circuits A and B respectively
and are active for 90 and 105 ton units only. The 90 and 105 ton
units have 3 compressors per circuit. If load conditions are such
that only one compressor is running on a circuit, a second com-
pressor is periodically turned on to equalize compressor oil lev-
els. If a second compressor is unavailable for oil return, the cir-
cuit will be shut down, and an alert will be generated. The alert
will automatically clear, and the circuit will restart when a sec-
ond compressor becomes available.
T051 (Circuit A, Compressor 1 Failure)
T052 (Circuit A, Compressor 2 Failure)
T053 (Circuit A, Compressor 3 Failure)
T059 (Circuit A, Compressor 4 Failure)
T054 (Circuit B, Compressor 1 Failure)
T055 (Circuit B, Compressor 2 Failure)
T056 (Circuit B, Compressor 3 Failure)
T060 (Circuit B, Compressor 4 Failure)
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 logged on the affected
compressor. If 3 successive strikes occur the compressor will be
locked out requiring a manual reset or power reset of the unit.
The clearing of strikes during compressor operation is a combi-
nation of 3 complete cycles or 15 continuous minutes of run
time operation. So, if there are one or 2 strikes on the compres-
sor and 3 short cycles (ON-OFF, ON-OFF, ON-OFF) occur in
less than 15 minutes, the strikes will be reset to zero for the af-
fected compressor. Also, if the compressor turns on and runs
for 15 minutes straight with no compressor failure, the com-
pressor's strikes are cleared as well.
NOTE: Until the compressor is locked out, for the first 2
strikes, the alert will not be broadcast to the network, nor will
the alarm relay be closed.
The possible causes are:
• High-pressure switch open. The high-pressure switch
(HPS) for each circuit is wired in series with the compres-
sor contactor coils of each compressor on the circuit to dis-
able compressor operation immediately upon a high dis-
charge pressure condition. If the high-pressure switch
opens while the MBB or CXB is commanding the com-
pressor ON, the compressor stops and the CSB no longer
detects current, causing the control to activate the alert.
• Compressor circuit breaker tripped.
• Failed CSB or wiring error.
To check out alerts T051, T052, T053, T054, T055, T056,
T059, T060:
1. Turn on faulty compressor using Service Test mode. If com-
pressor does not start, then most likely the problem is one of
the following: HPS open, compressor circuit breaker tripped,
incorrect control wiring, or incorrect compressor wiring.
2. If the compressor starts, verify that the indoor and outdoor
fans are operating properly.
3. If the CSB is always detecting current, then verify that the
compressor is on. If the compressor is ON, check the con-
tactor and the relay on the MBB or CXB. If the compres-
sor is OFF and there is no current, verify the CSB wiring
and replace if necessary.
4. Return to Normal mode and observe compressor operation
to verify that compressor current sensor is working and
condenser fans are energized.
A051 (Circuit A, Compressor 1 Stuck On Failure)
A052 (Circuit A, Compressor 2 Stuck On Failure)
A053 (Circuit A, Compressor 3 Stuck On Failure)
A059 (Circuit A, Compressor 4 Stuck On Failure)
A054 (Circuit B, Compressor 1 Stuck On Failure)
A055 (Circuit B, Compressor 2 Stuck On Failure)
A056 (Circuit B, Compressor 3 Stuck On Failure)
A060 (Circuit B, Compressor 4 Stuck On Failure)
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 and the HVAC Mode will display
Compressor Stuck On. These alarms are only monitored for a
period of 10 seconds after the compressor relay has been com-
manded OFF. This is done to facilitate a service technician
forcing a relay to test a compressor.
When the HVAC Mode indicates a compressor stuck on condi-
tion, the following will occur:
1. The outdoor fans will continue to control head pressure.
2. The supply fan will remain on.
3. Heating will be disabled.
A manual reset or power reset of the unit is required for these
alarms.
The possible causes are:
• Compressor contactor has failed closed.
• Relay output on MBB or CXB that drives compressor con-
tactor has failed closed.
• Failed CSB or wiring error.
To check out alarms A051, A052, A053, A054, A055, A056,
A059, A061:
1. Place the unit in Service Test mode. All compressors
should be OFF.
2. Check for welded compressor contactor.
3. Verify there is not 24 vac across the contactor coil of the
compressor in question. If 24 vac is measured across coil,
check relay on MBB or CXB and associated wiring.
4. Verify CSB wiring.
5. Return to Normal mode and observe compressor operation
to verify that compressor current sensor is working and
condenser fans are energized after compressor starts.
T057 (Circuit A, High Pressure Switch Trip Alert)
T058 (Circuit B, High Pressure Switch Trip Alert)
A057 (Circuit A, High Pressure Switch Trip Alarm)
A058 (Circuit B, High Pressure Switch Trip Alarm)
The high-pressure switch for each circuit is wired in series with
the compressor contactor coils of each compressor on the cir-
cuit to disable compressor operation immediately upon a high
discharge pressure condition. The normally closed contacts in
the switches are calibrated to open at 650 ± 10 psig which cor-
responds to a saturated condensing temperature of 155.6 ±
1.3°F. The pressure switches will automatically reset when the
discharge pressure is reduced to 500 ± 15 psig which corre-
sponds to a saturated condensing temperature of 134.1 ± 2.4°F.
The output of each high-pressure switch is wired to inputs on the
RXB to provide the control with an indication of a high-pressure
switch trip. This alarm could occur when compressors are off if
the wiring to the switch is broken or the switch has failed open.
If the high-pressure switch trips on a circuit with compressors
commanded on, the discharge pressure is recorded. If the recorded
discharge pressure is between 630 and 660 psig (saturated con-
densing temperature between 153.0 and 156.9°F), and is also less
than the value recorded on any previous high-pressure switch trip,
the upper horizontal portion of the compressor operating envelope
(see Fig. 17) is lowered 0.4°F (3 psig). The control will not allow
the compressor operating envelope to be lowered below 153.0°F
(630 psig).
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