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T-359
4–34
AL19
Discharge
Tempera-
ture High
Discharge tempera-
ture exceeds 135
C
(275
F) for 10 minutes
within the last hour.
Restrictions in the
refrigeration
system.
Ensure the Discharge
Service 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 refrig-
eration system.
With the unit off allow
system to stabilize to am-
bient temperature. Check
system pressure against
PT Chart for 134a, refer
to
Correct as required, refer
to Refrigerant Charge
.
Additional Alarms
such as AL16,
AL24.
Check compressor
operation.
If the alarm persists, it may
indicate a failing compres-
sor, replace the compres-
sor, refer to
COMPRESSOR
Service
AL20
Control Con-
tactor 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 resis-
tance at TP7 to TP9, if
short to ground, or if re-
sistance 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 in-
dicates a defective mi-
croprocessor.
Refer to Controller
Service
.
AL21
Control Cir-
cuit Fuse
(F1/F2)
One of the 18 VAC
controller fuses (F1/
F2) is open. Refer to
Cd08.
System Sensors
Check system sensors
for short to ground.
Replace defective
sensor(s)
Wiring
Check wiring for short to
ground.
Repair as needed.
Controller
Controller may have an
internal short.
Replace controller, refer to
Controller Service
AL22
Evaporator
IP
Evaporator motor in-
ternal protector (IP) is
open.
Evaporator Motor
Shut down unit, discon-
nect power, & check
Evaporator Motor IP at
plug connection
pins 4 & 6.
Replace defective
evaporator fan motor
refer to EVAPORATOR
FAN MOTOR
Service
.
AL23
Loss of
Phase B
Controller fails to
detect current draw.
Incoming Power
Check incoming
power source.
Correct power source as
required.
Table 4–6 Controller Alarm Indications
CODE #
CAUSE
COMPONENTS
TROUBLESHOOTING
CORRECTIVE ACTIONS
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