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Compressor Protection – Low Pressure Cutout Control
For each compressor/circuit, a Normally CLOSED low pressure cutout input will be monitored for
equipment protection on the Symbio 700. When a low pressure event is active, the input will become
OPEN and diagnostics will be generated as described below.
Prior to Compressor Startup:
If a compressor output is Off and its circuit’s LPC input is open, compressor operation will not be
inhibited. After compressor startup, the sequence described in the section below will be honored.
After Compressor Startup:
An LPC Bypass Delay function will delay the setting of a low pressure cutout after compressor startup on
a circuit until a pre-determined amount of time passes in low ambient conditions. The length of the
delay will be determined based on ambient temperature:
Outdoor Air Temperature Active < 40°F, the LPC Bypass Delay will be set to 60 seconds
50°F > Outdoor Air Temperature Active ≥ 40°F, the LPC Bypass Delay will be set to 30 seconds
Outdoor Air Temperature Active ≥ 50°F, the LPC Bypass Delay will be 0 seconds
After the LPC bypass timer has expired, following diagnostics will be generated based on the low
pressure cutout inputs for the unit
Circuit X LPC Trip (Auto-Reset):
For Cooling Only Units or Heat Pumps in Active Cooling:
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.
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.
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