AL15 - Loss of Cool. Alarm 15 is activated when SMV is greater than 15%, unit is in economized or standard operating modes and Return -- Supply Temperature Difference is less than 0.5C after 4 minutes of compressor run time. The alarm triggers failure action C ( evaporator fan only) or D ( all machinery off ) if in perishable mode and failure action D ( all machinery off ) if a frozen set point has been selected.. The alarm remains active until the unit is power cycled.