Evaporator coil - freeze condition - Johnson Controls - LIT-12011950 - Building automation software - Smart Equipment Controller - 5.0

Smart Equipment Controls Sequence of Operation Technical Bulletin

Johnson Controls
Product name
Smart Equipment Controller
Document type
Technical Bulletin
Document number
Revision date
Product status

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)
  • Freeze condition setpoint (Freeze-Sp)
  • Freeze condition lockout (FSi-LO for i=1 through 4)
  • Reset lockouts (ResetLO)


The input for the evaporator coil temperature is the 10k NTC type 3 thermistor for each installed cooling circuit evaporator (EC1, EC2, EC3, EC4).


The outputs include the following items:

  • Freeze condition (FSi for i=1 through 4)
  • Output relay for the appropriate refrigerant circuit (C1, C2, C3, C4)


If an evaporator temperature below the freeze condition setpoint (Freeze-Sp) is detected, the UCB sets the freeze condition (FS1, FS2, FS3, FS4) to true. If it is true, the UCB terminates any minimum compressor run time, de-energizes the compressor output relay, and starts the 5-minute ASCD. After the ASCD, the UCB energizes the compressor output relay as long as the evaporator temperature is above the freeze condition setpoint and there is still a call for Y. The default value for the freeze condition setpoint is 26 °F.

While the freeze condition is true, the compressor (Cx) does not run.

The UCB logs the first incident and tracks the run time. If the evaporator temperature alarms three times within 2 hours of run time, it locks out the compressor output relay and flags an alarm.

The exception to lockout of the compressor output relay is when the unit is operating in low ambient mode. In this mode a low evaporator coil temperature does not lock out the compressor. An error count of less than 3 is cleared and is not allowed to increment until after the low ambient mode disables. While low ambient is enabled and C1 is kept off because of the evaporator temperature, the LCD shows a status of low ambient rather than the freeze condition.

While FSx is True and preventing the compressor output relay from energizing, the fan remains on.

Any time a lockout occurs and Yx goes away, the lockout resets for one trip only and the alarm stops flashing on the LCD.

Off resets any FSx error counts less than 3 and stops any FSx LCD alarm. Three error counts produce a lockout.

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

Alarm reset occurs when the evaporator freezestat temperature reaches 39°F. The unit is not locked out on a critical alarm but the alarm remains in the alarm history.