How can you identify if a freeze stat has tripped on an air handler?

Identifying if a freeze stat has tripped on an air handler involves understanding its function. A freeze stat is designed to prevent freezing conditions in the air handler by shutting down the system when the temperature drops to a certain point.

When the freeze stat trips, it generally responds by sending a signal to close the outdoor dampers to prevent additional cold air from entering the system and further lowering the temperature inside the air handler. This action typically occurs while the fan is off, as the system seeks to halt the progression of freezing.

Thus, if you notice that the outdoor dampers are fully closed and the fan is not operating, it indicates that the freeze stat has activated to prevent potential damage to the system due to low temperatures. The other choices do not directly indicate a freeze stat trip: the temperature drop implies the issue but is not a definitive sign of activation; as for humidity levels rising or the compressor shutting down, these can occur for various reasons not strictly related to a freeze stat tripping.