Low pressure switch - Johnson Controls - LIT-12011950 - Building automation software - Smart Equipment Controller - 5.0

Smart Equipment Controls Sequence of Operation Technical Bulletin

Brand
Johnson Controls
Product name
Smart Equipment Controller
Document type
Technical Bulletin
Document number
LIT-12011950
Version
5.0
Revision date
2024-06-06
Product status
Active
Language
English

Setpoints and related data

The setpoints and related data include the following items:

  • Number of cooling stages installed (#ClgStgs)
  • Compressor stage command (Ci for i=1 through 4)
  • Low pressure limit (LPSi for i=1 through 4)
  • Low pressure lockout (LPSi-LO for i=1 through 4)
  • Low ambient cooling stages 10 on 5 off setpoint (LowAmb10On5OffSp)
  • Reset lockouts (ResetLO)
  • Operational outdoor air temperature (OprOAT)

Inputs

The input for the low pressure switch is contact closure from the appropriate refrigerant circuit low pressure switch (LPS1, LPS2, LPS3, LPS4).

Outputs

The output for the low pressure switch is the output relay for appropriate refrigerant circuit (C1, C2, C3, C4).

Operation

When this input is open, the compressor does not start unless in Low Ambient mode.

When the output relay has been energized, the low pressure switch does not affect the compressor output until the compressor has been running for the minimum time. If the operational outdoor air temperature is greater than the low ambient cooling stages 10 on 5 off setpoint, then the minimum time is 30 seconds. Otherwise it is 120 seconds and the limit for the low pressure switch trips toward a lockout is disabled. The low pressure switch does not lock out the compressors.

After the minimum time (30 seconds or 120 seconds), if the low pressure switch has been open or becomes open for more than 5 seconds, the UCB terminates any remaining minimum compressor runtime, de-energizes the output relay, and starts the ASCD. After the ASCD, the UCB turns on the compressor as long as there is still a call for Y and the low pressure switch has closed.

The UCB logs the first incident and tracks runtime. If not in low ambient conditions and the low pressure switch opens three times within one hour of run time, it locks out the compressor relay and displays an alarm on the LCD.

Note: To manually reset the lockout condition, navigate to the ResetLO point in the user interface and change the value from no to yes.