Abstract: An air conditioner suitable for use in a hazardous environment. The air conditioner, which may be of the conventional window type, is modified in such a manner that sparks are either eliminated, suppressed or contained to the extent that there is no danger of igniting an atmosphere that may contain an excess of dangerous particles. Any switching required in the electrical circuit is done by solid state devices, or with open contacts that carry such low power that sparking cannot occur, with the main load of the air conditioner being carried by the solid state device. The air conditioner is designed to withstand hostile elements such as salt spray from the ocean without excessive corrosion. A bypass valve is included to prevent frost collection on the evaporator coils if the air conditioner is unattended for long periods of time.

Abstract: The electrical control panel for a refrigeration unit using single or three phase power. The control portion has an oil pressure safety switch, defrost timer, temperature controls and perhaps a refrigerant pressure control in conjunction with the normal internal overload circuit breakers for the compressor. After operation of the refrigeration unit for a period of time, a defrost control device cuts off the compressor and turns on the electric defrost heaters. As the evaporator coils are defrosted, defrost thermostats open the defrost heater supply circuits. When the current sensing relay senses that all the defrost heaters have been shut off via the defrost thermostats, a time delay relay will return the refrigeration unit to the normal refrigeration cycle. The same current sensing relay will prevent false triggering by the oil pressure safety switch if the compressor's internal overload circuit breaker opens.