AAON VCCX-454 - A2 L Leak Detection Sequences

9VCCX-454 Controller Technical Guide
SAFETY
A2L Leak Detection Sequences
NOTE: The following sequences are only applicable with
a VCCX-454 connected to an A2L Mitigation
Controller. Refer to the A2L Mitigation Controller
Technical Guide for stand alone sequences.
NOTE: The A2L Leak Detect alarm will stay active on the
VCCX-454 even if the condition is cleared. It can only
be manually cleared by power cycling the VCCX-454
or by using the keypad and display on the VCCX-454.
Airstream Leak Detection Only
When the A2L Mitigation Board detects a leak in the airstream, all
compressor operations cease immediately and the A2L Leak Detect
alarm will be activated.
If the unit is commanded to be occupied
It will operate as it would normally with the compressors locked out.
If the unit is commanded unoccupied at any time while
the alarm is active
• The unit fan will be forced to operate based on the current
control method congured.
• Heating can operate as required; however, it will only
operate to the unoccupied control temperatures. The OA
damper is not required to open unless congured to operate
during Unoccupied Mode.
• If the HVAC Mode is SAT Tempering, Outdoor Air(MUA),
or DOAS Unit.
○ Operate the unit as if it were in Occupied Mode using
regular setpoints.
• If the HVAC Mode is Supply Air, Return Air, Space Temp,
Space Temp with High % OA, Single Zone VAV.
○ Operate the unit as if it were in Unoccupied Mode using
setback setpoints.
○ If Night Setbacks are set to 30ºF (disabling unoccupied
operation) run with Occupied setpoints.
Alarms related to compressors not operating should not be activated
as there are no issues with the compressors.
Cabinet Leak Detection Only
When the A2L Mitigation Board detects a leak in the cabinet, the A2L
Leak Detect alarm will be activated and the unit is commanded o.
Cabinet and Airstream Leak Detection
When the A2L Mitigation Board detects a leak in the cabinet and
the airstream, the A2L Leak Detect Alarm is activated.
If the unit is commanded to be occupied
It will operate as it would normally with the compressors and heat
locked out.
If the unit is commanded unoccupied at any time while
the alarm is active
• The unit fan will be forced to operate based on the current
control method congured.
• The OA damper is not required to open unless congured
to operate during Unoccupied Mode. If economizer cooling
is allowed, it will only operate to the unoccupied control
temperatures.
• If the HVAC Mode is SAT Tempering, Outdoor Air (MUA),
or DOAS Unit.
○ Operate the unit as if it were in Occupied Mode using
regular setpoints.
• If the HVAC Mode is Supply Air, Return Air, Space Temp,
Space Temp with High % OA, Single Zone VAV.
○ Operate the unit as if it were in Unoccupied Mode using
setback setpoints.
○ If Night Setbacks are set to 30ºF (disabling unoccupied
operation) run with Occupied setpoints.
Alarms related to compressors not operating should not be activated
as there are no issues with the compressors.