Review on Johnson Controls A421ABD 2C Electronic Temperature by Sherman Lancaster

I have 2 A419 and 1 A421. I've used them from time to time to control a smoker, a seedling heater, and a fan on a gas heater. The A419 is best suited for some applications because it has a differential setting that corresponds to a setpoint that needs to be changed frequently, e.g. B. when smoking fish, and I only have to make one adjustment each time. A 421 works well for a setpoint that stays fairly constant, like fan control for a heater. When using both A419 and A421 I have a contactor to finally turn on the heating elements for smoking. The sensors appear to be interchangeable which is a good feature as I have an "sF" error when smoking fish so I had a spare from one of the others that weren't being used.