A friend of mine wanted me to assemble a temperature control box for his gas valve. He chose the Johnson Control A419 to be the heart of his system. The controller has a digital display with adjustable differential. It can be used to heat or cool and features a wide setpoint temperature range (-30° F to 220° F) and differential adjustment (1° F to 3° F). The temperature sensor is a 1.94 inch thermistor on an 8 foot cable. The purpose of this build is to control the gas valve which fires the burner for the hot liquor tank.
The challenges I faced building this control box was different voltages. The A419 he purchased runs on 120 or 240 volts but the gas valve functions on 24 volts. This means that I needed to power the A419 with 120 volts and power the switched side with 24 volts.
This system was also designed for future additions. The goal was to make any future upgrades as easy to complete as possible. The plan for this box will be to add an additional controller, switches, and LED lights to the front of the panel. The lower portion of the control box will someday house two separate outlets which will run brewing pumps.
This control box consists of the box, a 24 volt transformer, a Johnson Controls A419 120/240 volt controller, two terminal blocks, and wire. Cost of materials is estimated at around $120.