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• All compressors on the associated circuit are de-energized immediately and they are locked out until
a Reset Diagnostic action is initiated.
• The “Diagnostic: Compressor X Proving Lockout” diagnostic point is activated and the alarm output
is activated.
Diagnostic: Compressor X Contactor Failure
If a compressor proving input becomes Active for 5 continuous seconds when the associated
compressor command output is Inactive, a Diagnostic: Compressor X Contactor Failure is generated
and the following occurs:
• All compressors on the associated circuit are de-energized immediately and they are locked out until
a Reset Diagnostic is initiated.
The “Compressor X Contactor Failure” diagnostic point is activated and the alarm output is activated.
Diagnostics – Low Pressure Cutout
The following operation is enforced based on the state of the circuit’s LPC input:
Prior to Compressor Startup:
• If a compressor output is Off and its circuit’s LPC input is open, compressor operation is not
inhibited, and the Diagnostic: Circuit X LPC Trip point will not be annunciated.
After Compressor Startup:
An LPC Bypass Delay function delays 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
is determined based on ambient temperature:
• If the Outdoor Air Temperature Active is less than 40°F, the LPC Bypass Delay is set to 60 seconds
• If the Outdoor Air Temperature Active is between 40°F and 50°F, the LPC Bypass Delay is set to 30
seconds
• If the Outdoor Air Temperature Active is greater than 50°F, the LPC Bypass Delay is 0 seconds
There are two diagnostics that can be generated based on the Compressor Low Pressure Cutout input:
Diagnostic: Circuit X LPC Trip
• All Compressors Outputs on the effected circuit are commanded OFF
• The Diagnostic: Circuit X LPC Trip point is annunciated
• The circuit is disabled for 3 minutes
• The circuit’s LPC trip counter is incremented
After the 3 minute low pressure event timeout has expired, if the unit is not under a lockout event,
• The Diagnostic: Circuit X LPC Trip point is reset
• If the stage is still requested ON, the circuit is allowed to stage again
• If the Circuit runs for 3 minutes, its LPC Trip Count is reset to 0.
On Heat Pumps, if the Outdoor Air Temperature is less than 0° F or if the unit is in active defrost, the low
pressure cutout input state is ignored.
Diagnostic: Circuit X LPC Lockout
If a circuit’s LPC trip counter accumulates 4 low pressure events without the circuit running for the 3
minute minimum on time (counter is not reset), a Diagnostic: Circuit X LPC Lockout” is generated.
Once a Diagnostic: Circuit X LPC Lockout has been generated, the following occurs:
• All compressors on the associated circuit are de-energized immediately and they are locked out until
a Reset Diagnostic is initiated.
• The Diagnostic: Circuit X LPC Lockout point is activated and the alarm output is activated.
Diagnostics
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