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ALr 20 - How the 'Return Air Under Temperature' alarm works

If the cooler temperature has dropped below the normal mode setpoint by a specified amount, the SCS Controller can switch off the compressor and other outputs to protect the asset and trigger an ALr 20 alarm.

Review the fault logic for the 'Return Air Under Temperature' alarm in the following graph:

'Return Air Under Temperature' alarm

Possible causes and actions

The temperature has dropped below the normal mode setpoint by a specified amount. The product temperature keeps getting colder, even when the compressor is turned off.

  1. Check the compressor is correctly wired, and that the “Compressor State” parameter is set correctly.

If this doesn't resolve the issue it may be due to an external secondary compressor relay failure.