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 size 090 and 100 units only. Size 090 and 100
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 levels.
If a second compressor is unavailable for oil return, the circuit will
be shut down, and an alert will be generated. The alert will auto-
matically clear, and the circuit will restart when a second compres-
sor becomes available.
T051 (Circuit A, Compressor 1 Failure)
T052 (Circuit A, Compressor 2 Failure)
T053 (Circuit A, Compressor 3 Failure)
T054 (Circuit B, Compressor 1 Failure)
T055 (Circuit B, Compressor 2 Failure)
T056 (Circuit B, Compressor 3 Failure)
If the current sensor board reads OFF while the compressor relay
has been commanded ON for a period of 4 continuous seconds, an
alert is generated.
Any time this alert occurs, a strike will be logged on the affected
compressor. If three 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 combina-
tion of 3 complete cycles or 15 continuous minutes of run time op-
eration. So, if there are one or two strikes on the compressor and
three short cycles (ON-OFF, ON-OFF, ON-OFF) occur in less
than 15 minutes, the strikes will be reset to zero for the affected
compressor. Also, if the compressor turns on and runs for 15 min-
utes 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 open. The high pressure switch for
each circuit is wired in series with the compressor
contactor coils of each compressor on the circuit to disable
compressor operation immediately upon a high discharge
pressure condition. If the high pressure switch opens while
the MBB or CXB is commanding the compressor 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:
1. Turn on faulty compressor using Service Test mode. If the
compressor does not start, then most likely the problem is
one of the following: HPS is open, compressor circuit
breaker is 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)
A054 (Circuit B, Compressor 1 Stuck On Failure)
A055 (Circuit B, Compressor 2 Stuck On Failure)
A056 (Circuit B, Compressor 3 Stuck On Failure)
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 and the HVAC Mode will display Compres-
sor Stuck On. 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.
When the HVAC Mode indicates a compressor stuck on condition,
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.
A643 Ht Coil Act Ovrload, Setpt Pos Not Reached Alarm only Automatic
A644 Heat Coil Actuator Hunting Excessively Alarm only Automatic
A650 Bldg.Press. Actuator 1 Out of Calibration Alarm only Automatic
A651 Bldg.Press. Actuator 1 Comm Failure No building pressure control Automatic
T652 Bldg.Press. Act. 1 Control Range Increased Alert only Automatic
A653 BP Act. 1 Overload, Setpnt Pos Not Reached Alarm only Automatic
A654 Bldg.Press. Actuator 1 Hunting Excessively Alert only Automatic
A660 Bldg.Press. Actuator 2 Out of Calibration Alarm only Automatic
A661 Bldg.Press. Actuator 2 Comm Failure No building pressure control Automatic
T662 Bldg.Press. Act. 2 Control Range Increased Alert only Automatic
A663 BP Act. 2 Overload, Setpnt Pos Not Reached Alarm only Automatic
A664 BP Actuator 2 Hunting Excessively Alert only Automatic
A700 Air Temp Lvg Supply Fan Thermistor Failure Unit shut down Automatic
T701 Staged Heat 1 Thermistor Failure Average remaining sensors Automatic
T702 Staged Heat 2 Thermistor Failure Average remaining sensors Automatic
T703 Staged Heat 3 Thermistor Failure Average remaining sensors Automatic
A704 Staged Heat Lvg Air Temp Sum Total Failure No staged heat function Automatic
T705 Limit Switch Thermistor Failure No software limit switch function Automatic
A706 Hydronic Evap Discharge Thermistor Failure Unit shut down Automatic
T707 Digital Scroll Discharge Temperature Failure Digital compressor A1 limited to 50% Automatic
T800 Cannot Enable MLV and Digital Scroll Simultaneously Alert; Incorrect unit configuration Automatic
Table 106 — Alert and Alarm Codes (cont)
ALARM OR
ALERT NUMBER
DESCRIPTION ACTION TAKEN BY CONTROL RESET METHOD
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