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For Heat Pump Units in Active Mechanical Heating and Outdoor Air Temperature ≥ 0°F
If a compressor low pressure cutout input opens:
All Compressor Outputs on the effected circuit will be immediately Commanded OFF.
The “Circuit X LPC Trip” diagnostic point will be annunciated.
The Circuit will be disabled for 3 minutes.
The Circuit’s LPC trip count will be incremented.
On Heat Pumps, if the Outdoor Air Temperature is < 0°F or if the unit is in active Defrost, the low
pressure cutout diagnostic is ignored. This is to allow a heat pump to continue to provide heating
capacity at low ambient conditions.
After the 3 minute low pressure event timeout has expired, if the unit is not under a “Circuit Lockout”
event:
The “Circuit X LPC Trip” diagnostic will be reset
If the cooling stage is still requested ON, the circuit will be allowed to stage again.
If the Circuit runs for 3 minutes, its LPC Trip Count will be reset to 0.
Circuit “X” Low Pressure Lockout (Manual Reset)
If a compressor/circuit accumulates 4 “Circuit X Low Pressure Trips” without the circuit running for the
3-minute minimum on time (counter is not reset), a “Circuit X LPC Lockout” will be generated.
Once the lockout is generated the circuit will be locked out until a Diagnostic Reset is initiated.
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