An absorption chiller having a protection system for preventing the chilled water in the evaporator tubes from freezing in the event the water flow through the tubes closes down while the machine is running. The received signal is analyzed and conditions the control valve for opening if watering criteria is met. When used as a microphone the transducer is substantially insensitive to vibrations, and when used as a speaker the transducer generates only very low vibration levels. A phase-change material having constructive change in phase and thickness is deposited over the polycarbonate material to create the disk.