Carrier Weathermaster 48P030-100 Controls, Start-Up, Operation, Service, And Troubleshooting page 126

To check out alerts A051, A052, A053, A054, A055, A056:
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 Failure Alert)
T058 (Circuit B, High Pressure Switch Failure Alert)
A057 (Circuit A, High Pressure Switch Failure Alarm)
A058 (Circuit B, High Pressure Switch Failure Alarm)
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. The normally closed contacts in the switches
are calibrated to open at 650 ± 10 psig which corresponds to a sat-
urated 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 corresponds to a saturated con-
densing 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 to 660 psig (saturated condens-
ing 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
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Fig. 17 — High Pressure/SCT Alarm Upper 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).
This is done to make a rough calibration of the high pressure
switch trip point. In most cases this allows the control to detect a
high head pressure condition prior to reaching the high pressure
switch trip point.
When the trip occurs, all mechanical cooling on the circuit is shut
down until the HPS is cleared for 15 minutes. Any time this alert
occurs, a HPS trip strike will be logged on the affected circuit. The
alert is issued on HPS trip strikes 1 and 2, and an alarm (A057,
A058) is issued on strike 3.
An active alert or alarm will always cause the circuit to be shut
down. After 15 minutes, the circuit is allowed to restart if there are
fewer than 3 strikes on the affected circuit. If three successive
strikes occur the circuit will be locked out, requiring a manual re-
set or power reset of the unit. The clearing of HPS trip strikes
during compressor operation is achieved through 5 continuous
minutes of run time on the affected circuit. So, if there are one or
two strikes on the circuit and a compressor on the circuit turns on
and runs for 5 minutes straight with no failure, the circuit's HPS
trip strikes are cleared.
NOTE: This alert/alarm is broadcast to the network.
T068 (Circuit A Return Gas Thermistor Failure)
This alert trips during a thermistor failure of the return gas tem-
perature sensor. It is used with MLV option only.
T072 (Evaporator Discharge Reset Sensor Failure)
This sensor is responsible for third-party reset of the cooling
supply air set point. If the unit is configured for "third-party re-

set" (Configuration
no reset will be applied to the cooling supply air set point. Re-
covery from this alert is automatic. Reason for error is either a
faulty sensor, wiring error, or damaged input on the CEM board.
20 30 40
SST (°F)
126
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EDT.R RS.CF=3) and this alert occurs,
50 60 70 80