Solid-State Controller for Air Conditioning Units

It is essential to maintain the condensing temperature of air-cooled air conditioning systems at certain minimum levels when operating during cold weather. Recent advances in solid-state technology have opened up new approaches to controlling condensing temperatures at any desired minimum level. The solid-state control system described uses an SCR with a unijunction transistor firing circuit to control directly the power to the specially designed fan motors. In designing such a control system, consideration has to be given to matching properly the solid-state control, fan motor, and the temperature sensing device with the air conditioning unit performance characteristics to obtain the desired reliability and stability.