Circuit A Low Superheat; Circuit A Low Cooler Suction Temperature; Circuit A, High Pressure Switch Failure; Circuit A High Head Pressure - Carrier AquaSnap 30MPA Series Controls, Start-Up, Operation, Service, And Troubleshooting

A114 (Circuit A Low Superheat) — Alarm code 114 occurs
when the superheat of a circuit is less than 5 F (2.8 C) for 5
continuous minutes. The low superheat alarm is generated and
the circuit is shut down. The RGT sensor must be installed.
A116 (Circuit A Low Cooler Suction Temperature) —
Alarm code 116 occurs when mode 7 causes the compressor to
unload 3 consecutive times in less than 30-minute intervals be-
tween each circuit shutdown. The low cooler suction tempera-
ture alarm is generated and the circuit is shut down. If this con-
dition is encountered, check the following items:
• Check for a faulty expansion valve.
• Check for a plugged filter drier.
• Check for a low refrigerant charge condition.
• Check the suction pressure transducer for accuracy.
• Check the cooler flow rate.
• Check the chilled water strainer for a restriction.
• Consider a fouled cooler.
• Check the glycol concentration in the loop; high glycol
concentrations can cause the same effect as a fouled
cooler.
• Check that the water flow is in the proper direction.
P118 — High Discharge Gas Temperature
T118 — High Discharge Gas Temperature
Criteria for Trip: This alert is part of the compressor protection
algorithm for digital compressor units. The following condi-
tions must be true:
1. This alert will be triggered if the unit has a digital com-
pressor and it is enabled (Configuration
A1.TY=YES).
2. The discharge gas temperature (Temperatures

CIR.A D.GAS) is greater than 268 F (131.1 C).
Action To Be Taken: Compressor A1 is shut down. If this is the
first or second occurrence within a 32-minute window, the pre-
alert P118 will be generated. This is a non-broadcast alert. If
this is the third occurrence within the 32-minute window, the
alert T118 is generated.
Reset Method: The first two times compressor A1 is shut down
due to the pre-alert P118, the pre-alert will automatically reset
after the discharge temperature is less than 250 F (121.1 C) and
the compressor will restart. The third occurrence will result in
the alert T118 and will require a manual reset.
Multiple P118 pre-alerts may be stored in the alarm history.
If there are 1 or 2 strikes on the circuit and the circuit recovers
for a period of time, it is possible to clear out the strikes, there-
by resetting the strike counter automatically.
Possible Causes: If this condition is encountered, check the
following items:
• Check to be sure that the circuit is properly charged. If a
leak is found, repair the leak and recharge the circuit.
• Check the discharge temperature thermistor (DTT) for
accuracy.
• Check the discharge temperature thermistor (DTT) con-
nections.
• Check unit configuration. A1.TY = NO if no digital com-
pressor is installed.
A122 (Circuit A, High Pressure Switch Failure) — The
high-pressure switch is wired in series with the compressor
contactor coils of each compressor on the circuit to disable
compressor operation immediately upon a high discharge pres-
sure condition.
For all 30MP015-045, 30MPA050-071, and 30MP050-071
high condensing units: The normally closed contacts in the
switches are calibrated to open at 650 ± 10 psig (448.2 ± 68.9
kPag) which corresponds to a saturated condensing tempera-
ture of 155.6 ± 1.3 F (68.7 ± 0.7 C). The pressure switches will
automatically reset when the discharge pressure is reduced to
500 ± 15 psig (3448 ± 103.4 kPag) which corresponds to a sat-
urated condensing temperature of 134.1 ± 2.4 F (56.7 ± 1.3 C).
For all 30MPW050-071 standard units: The normally
closed contacts in the switches are calibrated to open at 558 ±
10 psig (3847 ± 68.9 kPag) which corresponds to a saturated
condensing temperature of 140.3 ± 2.3 F (60.16 ± 16.5 C). The
pressure switches will automatically reset when the discharge
pressure is reduced to 435 ± 29 psig (2999 ± 199.9 kPag)
which corresponds to a saturated condensing temperature of
120.35 ± 5.3 F (49.08 ± 14.83 C).
The output of the high-pressure switch is wired to inputs on
the MBB to provide the control with an indication of a high
pressure switch trip. This alert could occur when compressors
are off if the wiring to the switch is broken or the switch has
failed open.
When the trip occurs, all mechanical cooling on the circuit
is shut down for 15 minutes. After 15 minutes, the circuit is al-
lowed to restart.
A126 (Circuit A High Head Pressure) — This alarm occurs
when the appropriate saturated condensing temperature is
greater than the operating envelope shown in Fig 43-45. Prior
to the alarm, the control will shut down one compressor on a
circuit if that circuit's saturated condensing temperature is
greater than the maximum SCT minus 5° F (2.7° C). If SCT
continues to rise to greater than the maximum SCT, the alarm
will occur and the circuit's remaining compressor will shut
down. The cause of the alarm is usually an overcharged sys-
tem, high outdoor ambient temperature coupled with dirty out-
door coil (30MPA only), plugged filter drier, a faulty high-pres-
sure switch, faulty expansion valve, or loss of condenser water
 
UNIT
flow. Figures 43-45 shows the operating envelope for the
compressor.

This alarm is also generated when the saturated suction tem-
perature is below the low limit for compressors (outside of
compressor envelope).
If this condition is encountered, check the following items:
• Check to be sure that the circuit is properly charged. If a
leak is found, repair the leak and recharge the circuit.
• Check for proper water flow for the cooler.
• For 30MPA units, if the alarms are occurring during cold
ambient conditions, consider installing head pressure
control on remote condenser.
• If wind baffles are required, check to see if they are
installed.
• Check the suction pressure transducer accuracy.
• Check for a low load condition. Check the control sys-
tem to see if the unit should be operating.
• Check for restrictions in the liquid line. Be sure all ser-
vice valves are open.
• Check the filter drier. Change the core(s) if necessary.
• Check glycol concentration and make sure brine freeze
(Set Points
centration.
• Check the operation of the liquid line solenoid valves, if
equipped. Be sure that the correct valve operates for the
circuit.
• Be sure that the liquid line solenoid valve is installed cor-
rectly (flow), if equipped.
• For the circuit TXV(s):
- Check the superheat setting of the TXV. A very high set-
ting will cause low saturated suction condition.
- Check to be sure the proper TXV is installed.
- Check the operation of the TXV.
- Check the location of the TXV bulb and that it is properly
installed on the suction line.
- Check the TXV equalizer line to be sure that it is properly
connected to the suction line and open to suction pressure.
65
 
FRZ BR.FZ) is properly set for the con-