20
Flash
Code
ActionsPossible CausesMode
Reset
Time
Amber LED DescriptionTy p e
72 Local
SUCTION OVER TEMPERA-
TURE EVENT
(elevates to fault code 82 after
3 occurrences)
15 Minutes Both See fault 82 Same actions for 82
74
System
Malfunction
DISCHARGE TEMP OUT OF
RANGE LOCKOUT
(Elevated from fault code 59 af-
ter 5 occurrences)
2 Hours
Both
Sensor Harness not
connected to AOC
control
Ensure plug is connected to AOC control
Broken or loose
harness wire
Check harness for continuity; see resistance
chart to check resistance at given temperature
Broken or Damaged
Sensor
Check harness for continuity; see resistance
chart to check resistance at given temperature
Hardware damage to
AOC control
Replace AOC control
Indoor Unit Airflow too
low or off
Troubleshoot indoor fan motor and make sure
it is working
Outdoor Unit Airflow too
low or off
Troubleshoot outdoor fan motor and make
sure it is working
Reversing Valve By-
pass or Reversing
Valve not energized
Reversing Valve stuck halfway
Ensure AOC fuse is good
24 VDC in cooling mode
Check harness and connectors
Cool High Load conditions Over charge: Check system charge
Heat
Low Charge or Loss of
Charge at low ambient
heating conditions
Undercharged or No charge: check charge
Heat
Expansion Device
Restriction
Heating: Trouble shoot EXV (coil, harnesses);
Trouble shoot the TXV
Power Cycle system, is EXV moving on power
up (audible)
75 Local
MAXIMUM POWER MODE -
TEMP
(Temporary RPM reduction or
stage lowering will result.)
NA Both
Outdoor Airflow too low
or off
Check ODU coil for clogging (ice or debris)
and clean if necessary; Troubleshoot ODU fan
motor and make sure it is working
Blocked Inverter Heat
Exchanger (fins)
Check Inverter fins for debris and clean if nec-
essary
Application violates
guideline
Consult Application Guideline for compliance
76
System
Malfunction
FAN INVERTER LOCKOUT
(Elevated from fault code 61
after 5 occurrences)
2 Hours Both
Fan blade bent/out of
balance
Check outdoor fan blade
Check for ice build up
Fan blade restricted
Check outdoor fan blade clearance
Check for ice build up
Fan motor wiring
Check outdoor fan motor connectors and har-
ness
Fan motor Replace outdoor fan motor
Inverter damage Replace inverter
77 Local
MAXIMUM POWER MODE -
COMP CURRENT
(Temporary RPM reduction or
stage lowering will result.
NA Both
Compressor is operat-
ing outside the allowed
operational envelope
Inverter will reduce speed to a lower stage
Incorrect refrigerant
charge
Check refrigerant amount
Outdoor Airflow too low
or off
Check ODU coil for clogging (ice or debris)
and clean if necessary; Troubleshoot ODU fan
motor and make sure it is working
Incoming power supply
voltage
Check voltage versus unit rating plate for
allowable range
Loose or incorrect wire
connections
Check incoming power leads and leads to the
compressor plug
79 Local
COMPRESSOR/INVERTER
FAULT
(Elevates to fault code 88 after
5 occurrences)
6 Minutes Both
Compressor fails to
start
System will try to self-mitigate with repeated
start attempts
82
System Mal-
function
SUCTION OVER TEMP
LOCKOUT
(Elevated from fault code 72 af-
ter 3 occurrences)
4 Hours
Both
Incorrect refrigerant
charge
Check refrigerant amount
Cool Uninsulated vapor line Insulate the vapor line
Cool Indoor TXV operation Troubleshoot TXV
Heat Outdoor EXV operation Troubleshoot EXV
Both Reversing valve bypass troubleshoot reversing valve
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