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3 − 28 T-364
Table 3 − 6 Controller Alarm Indications (Sheet 3 of 8)
Alarm Code Cause Components Troubleshooting Corrective Actions
AL18
Discharge
Pressure High
Discharge pressure is
over the maximum for
10 minutes within the
last hour.
Restrictions in the
refrigeration
system.
Ensure Liquid Line Service
Valve is fully open.
Open Liquid Line Ser-
vice Valve as needed.
Filter Drier Check the filter drier, if it is
iced up or very cold it
indicates that the filter drier
needs replacement.
Replace the filter drier if
needed, refer to FILTER
DRIER Service Section
6.12.
Condenser Fan Check Condenser Fan for
proper operation.
Correct as required.
Discharge
Pressure
Transducer (DPT)
Confirm accurate DPT
pressure readings, refer to
MANIFOLD GAUGE SET
Section 6.2.
Replace DPT if
defective.
Non-condens-
ables in the refri-
geration system.
With the unit off allow
system to stabilize to
ambient temperature.
Check system pressure
against PT Chart for 134a,
refer to Table 6 − 4.
Correct as required,
refer to Refrigerant
Charge Section 6.7.1.
Refrigerant Check refrigerant level. Correct as required,
refer to Refrigerant
Charge Section 6.7.1.
AL19
Discharge
Temperature
High
Discharge temperat-
ure exceeds 135 C
(275 F) for 10 minutes
within the last hour.
Restrictions in the
refrigeration
system.
Ensure the Discharge Ser-
vice Valve is fully open.
Open the Discharge Ser-
vice Valve as needed.
Check the unit for air flow
restrictions.
Clean or remove any
debris from coils.
Non-condens-
ables in the refri-
geration system.
With the unit off allow
system to stabilize to
ambient temperature.
Check system pressure
against PT Chart for 134a,
refer to Table 6 − 4.
Correct as required,
refer to Refrigerant
Charge Section 6.7.1.
Additional Alarms
such as AL16,
AL24.
Check compressor
operation.
If the alarm persists, it
may indicate a failing
compressor, replace the
compressor, refer to
COMPRESSOR Ser-
vice Section 6.8.
AL20
Control
Contactor
Fuse (F3)
Control power fuse
(F3A or F3B) is open.
Check F3A, if the
fuse is open:
Check PA, PB, CH coils for
short to ground, if short is
found:
Replace the defective
coil.
Replace the fuse.
Check F3B, if the
fuse is open:
Check ESV coil resistance
at TP7 to TP9, if short to
ground, or if resistance is
less than 4 ohms, coil is
defective.
Check CF, ES, EF, HR coils
for short to ground, if short
is found, coil is defective.
Replace the defective
coil.
Replace the fuse.
Check Voltage at
QC1:
If voltage is present, it
indicates a defective
microprocessor.
Refer to Controller
Service Section 6.21.