R502

The R502 specification describes a heater delay timer board that controls a line-voltage heater from a thermistor. It accumulates the time the thermistor is between LoTemp and HiTemp, with 25 F and 40 F given as the example, and energizes the relay when that time reaches a preset of 0, 3, 6, or 12 hours. The relay stays on until HiTemp, then the board selects the next lower hour setting. An example RstTemp of 55 F resets the board to 6 hours. An LED shows the period in force, or a thermistor short or open.

LED codes on the sheet are 1 blink for 12 hours, 2 blinks for 6 hours, 3 blinks for 3 hours, 4 blinks for 0 hours, and a continuous flash for a shorted or open thermistor. The board comes with a 10K ohm thermistor on a 3 foot (1 meter) lead that plugs into the screw terminals. Electrical ratings are a nominal 24 Vac input, 18 to 30 Vac operating range, and outputs of 12 FLA (30 LRA) at 240 Vac. PCB size is 3.5 by 2.125 inches. The sheet is dated 3-10-25.