Page 57
31-5000751 Rev. 0
High Pressure Switch and Low Pressure Protection Errors
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Component or System Operational State and Troubleshooting Tip
How to Clear Alert
Code
410
Information
Only-Dealer
OD Open Low
Pressure Switch
Unit low pressure is below the required limit.
Check operating pressures.
Low pressure switch opens at a specific pressure (system shuts down) and closes at a
specific pressure (system restarts).
Automatically clears
when the system
detects that the issue
no longer exists.
411
Service
Urgent
OD Low Pressure
Switch Strikes
Lockout
The low pressure switch has opened five times during one cooling or heating demand.
Thermostat will shut down the outdoor unit.
Open low pressure switch error count reached five strikes.
Check system charge using both approach and sub-cooling methods.
Reset by putting outdoor unit control in test mode or resetting low voltage power.
Automatically clears
when the system
detects that the issue
no longer exists.
412
Information
Only-Dealer
OD Open High
Pressure Switch
The unit high pressure is above the upper limit.
System will shut down.
Confirm that the system is properly charged with refrigerant.
Check condenser fan motor, expansion valve (if installed), indoor unit blower motor, stuck
reversing valve or clogged refrigerant filter.
Confirm that the outdoor unit is clean.
Automatically
clears after the high
pressure switch
closes or a power
reset.
413
Service
Urgent
OD High Pressure
Switch Strikes
Lockout
The high pressure switch has opened five times during one cooling demand.
Thermostat will shut down the outdoor unit.
Open high pressure switch error count reached five strikes.
Check system charge using superheat and sub-cooling temperatures.
Check outdoor fan operation.
Check for dirt or debris blocking air flow to outdoor unit.
Reset by putting outdoor unit control in test mode or resetting low voltage power.
Automatically clears
when the system
detects that the issue
no longer exists.
Table 18. Alert Codes and Troubleshooting
Compressor Operation, Checkout and Status / Error Codes
OPERATION:
The NS18HM uses two different types of compressor, depending on the specific model. The NS18HM36 uses a 380VAC
three phase variable capacity rotary compressor specifically designed for unitary splits system and is approved for use
with HFC 410A refrigerant. The NS18HM60 units use a 380VAC three phase variable capacity scroll compressor that is
approved for use with HFC 410A refrigerant. The compressor, when connected to an inverter, is capable of operating in a
running frequency range from 20 hertz up to a maximum of 78 hertz. (maximum hertz is dependent on compressor size and
operating mode). The compressor speed is determined by thermostat demand and suction pressure when installed with a
conventional 24VAC thermostat.
CHECKOUT:
NOTE:
The compressor motor winding resistance is the nominal resistance at 77F. When measuring compressor motor
winding resistance, the primary concern is the winding resistance between the different sets of terminals is within 10% of
each other. The actual winding resistance is impacted by temperature, refrigerant and oil. Do not automatically condemn
a compressor because the measured resistance is slightly higher or lower than the nominal resistance. Check for shorted/
open windings and for shorts to ground during testing.